From bd234ed89042726876d2460b5aab07ce43fd25a9 Mon Sep 17 00:00:00 2001
From: Valentyn Kolesnikov <javadev75@gmail.com>
Date: Sun, 3 Dec 2023 12:41:47 +0200
Subject: [PATCH] Added tasks 3-10

---
 .../php/g0001_0100/s0001_two_sum/Solution.php |   1 -
 .../Solution.php                              |  41 +++++++
 .../readme.md                                 |  40 +++++++
 .../Solution.php                              |  52 ++++++++
 .../readme.md                                 |  50 ++++++++
 .../Solution.php                              |  42 +++++++
 .../readme.md                                 |  34 ++++++
 .../s0006_zigzag_conversion/Solution.php      |  38 ++++++
 .../s0006_zigzag_conversion/readme.md         |  39 ++++++
 .../s0007_reverse_integer/Solution.php        |  23 ++++
 .../s0007_reverse_integer/readme.md           |  35 ++++++
 .../s0008_string_to_integer_atoi/Solution.php |  44 +++++++
 .../s0008_string_to_integer_atoi/readme.md    | 113 ++++++++++++++++++
 .../s0009_palindrome_number/Solution.php      |  39 ++++++
 .../s0009_palindrome_number/readme.md         |  41 +++++++
 .../Solution.php                              |  39 ++++++
 .../readme.md                                 |  56 +++++++++
 .../SolutionTest.php                          |  19 +++
 .../SolutionTest.php                          |  15 +++
 .../SolutionTest.php                          |  15 +++
 .../s0006_zigzag_conversion/SolutionTest.php  |  15 +++
 .../s0007_reverse_integer/SolutionTest.php    |  19 +++
 .../SolutionTest.php                          |  27 +++++
 .../s0009_palindrome_number/SolutionTest.php  |  19 +++
 .../SolutionTest.php                          |  27 +++++
 25 files changed, 882 insertions(+), 1 deletion(-)
 create mode 100644 src/main/php/g0001_0100/s0003_longest_substring_without_repeating_characters/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0003_longest_substring_without_repeating_characters/readme.md
 create mode 100644 src/main/php/g0001_0100/s0004_median_of_two_sorted_arrays/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0004_median_of_two_sorted_arrays/readme.md
 create mode 100644 src/main/php/g0001_0100/s0005_longest_palindromic_substring/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0005_longest_palindromic_substring/readme.md
 create mode 100644 src/main/php/g0001_0100/s0006_zigzag_conversion/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0006_zigzag_conversion/readme.md
 create mode 100644 src/main/php/g0001_0100/s0007_reverse_integer/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0007_reverse_integer/readme.md
 create mode 100644 src/main/php/g0001_0100/s0008_string_to_integer_atoi/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0008_string_to_integer_atoi/readme.md
 create mode 100644 src/main/php/g0001_0100/s0009_palindrome_number/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0009_palindrome_number/readme.md
 create mode 100644 src/main/php/g0001_0100/s0010_regular_expression_matching/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0010_regular_expression_matching/readme.md
 create mode 100644 src/test/php/g0001_0100/s0003_longest_substring_without_repeating_characters/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0004_median_of_two_sorted_arrays/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0005_longest_palindromic_substring/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0006_zigzag_conversion/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0007_reverse_integer/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0008_string_to_integer_atoi/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0009_palindrome_number/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0010_regular_expression_matching/SolutionTest.php

diff --git a/src/main/php/g0001_0100/s0001_two_sum/Solution.php b/src/main/php/g0001_0100/s0001_two_sum/Solution.php
index 9fc3f92..dd0c725 100644
--- a/src/main/php/g0001_0100/s0001_two_sum/Solution.php
+++ b/src/main/php/g0001_0100/s0001_two_sum/Solution.php
@@ -7,7 +7,6 @@
 // #2023_11_29_Time_9_ms_(97.47%)_Space_19.8_MB_(77.40%)
 
 class Solution {
-
     /**
      * @param Integer[] $nums
      * @param Integer $target
diff --git a/src/main/php/g0001_0100/s0003_longest_substring_without_repeating_characters/Solution.php b/src/main/php/g0001_0100/s0003_longest_substring_without_repeating_characters/Solution.php
new file mode 100644
index 0000000..d10133e
--- /dev/null
+++ b/src/main/php/g0001_0100/s0003_longest_substring_without_repeating_characters/Solution.php
@@ -0,0 +1,41 @@
+<?php
+
+namespace leetcode\g0001_0100\s0003_longest_substring_without_repeating_characters;
+
+// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #String #Hash_Table #Sliding_Window
+// #Algorithm_I_Day_6_Sliding_Window #Level_2_Day_14_Sliding_Window/Two_Pointer #Udemy_Strings
+// #Big_O_Time_O(n)_Space_O(1) #2023_12_03_Time_4_ms_(99.33%)_Space_19.1_MB_(68.83%)
+
+class Solution {
+    /**
+     * @param String $s
+     * @return Integer
+     */
+    public function lengthOfLongestSubstring($s) {
+        $lastIndices = array_fill(0, 256, -1);
+        $maxLen = 0;
+        $curLen = 0;
+        $start = 0;
+
+        for ($i = 0; $i < strlen($s); $i++) {
+            $cur = $s[$i];
+            $curAscii = ord($cur);
+
+            if ($lastIndices[$curAscii] < $start) {
+                $lastIndices[$curAscii] = $i;
+                $curLen++;
+            } else {
+                $lastIndex = $lastIndices[$curAscii];
+                $start = $lastIndex + 1;
+                $curLen = $i - $start + 1;
+                $lastIndices[$curAscii] = $i;
+            }
+
+            if ($curLen > $maxLen) {
+                $maxLen = $curLen;
+            }
+        }
+
+        return $maxLen;
+    }
+}
diff --git a/src/main/php/g0001_0100/s0003_longest_substring_without_repeating_characters/readme.md b/src/main/php/g0001_0100/s0003_longest_substring_without_repeating_characters/readme.md
new file mode 100644
index 0000000..bf1ef46
--- /dev/null
+++ b/src/main/php/g0001_0100/s0003_longest_substring_without_repeating_characters/readme.md
@@ -0,0 +1,40 @@
+3\. Longest Substring Without Repeating Characters
+
+Medium
+
+Given a string `s`, find the length of the **longest substring** without repeating characters.
+
+**Example 1:**
+
+**Input:** s = "abcabcbb"
+
+**Output:** 3
+
+**Explanation:** The answer is "abc", with the length of 3. 
+
+**Example 2:**
+
+**Input:** s = "bbbbb"
+
+**Output:** 1
+
+**Explanation:** The answer is "b", with the length of 1. 
+
+**Example 3:**
+
+**Input:** s = "pwwkew"
+
+**Output:** 3
+
+**Explanation:** The answer is "wke", with the length of 3. Notice that the answer must be a substring, "pwke" is a subsequence and not a substring. 
+
+**Example 4:**
+
+**Input:** s = ""
+
+**Output:** 0 
+
+**Constraints:**
+
+*   <code>0 <= s.length <= 5 * 10<sup>4</sup></code>
+*   `s` consists of English letters, digits, symbols and spaces.
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0004_median_of_two_sorted_arrays/Solution.php b/src/main/php/g0001_0100/s0004_median_of_two_sorted_arrays/Solution.php
new file mode 100644
index 0000000..ca60cbc
--- /dev/null
+++ b/src/main/php/g0001_0100/s0004_median_of_two_sorted_arrays/Solution.php
@@ -0,0 +1,52 @@
+<?php
+
+namespace leetcode\g0001_0100\s0004_median_of_two_sorted_arrays;
+
+// #Hard #Top_100_Liked_Questions #Top_Interview_Questions #Array #Binary_Search #Divide_and_Conquer
+// #Big_O_Time_O(log(min(N,M)))_Space_O(1) #2023_12_03_Time_23_ms_(88.34%)_Space_19.1_MB_(87.47%)
+
+class Solution {
+    /**
+     * @param Integer[] $nums1
+     * @param Integer[] $nums2
+     * @return Float
+     */
+    function findMedianSortedArrays($nums1, $nums2) {
+        $nums3 = [];
+        $sum = count($nums1) + count($nums2);
+        $med = ($sum / 2);
+        if ($sum % 2 === 0) {
+            $index = [$med - 1, $med];
+        } else {
+            $index = [floor($med)];
+        }
+        $i = 0;
+        $i1 = 0;
+        $i2 = 0;
+        while ($i < $sum) {
+            if (!isset($nums1[$i1])) {
+                $nums3[] = $nums2[$i2];
+                $i2++;
+                $i++;
+                continue;
+            }
+            if (!isset($nums2[$i2])) {
+                $nums3[] = $nums1[$i1];
+                $i1++;
+                $i++;
+                continue;
+            }
+            if ($nums1[$i1] < $nums2[$i2]) {
+                $nums3[] = $nums1[$i1];
+                $i1++;
+            } else {
+                $nums3[] = $nums2[$i2];
+                $i2++;
+            }
+            $i++;
+        }
+        return isset($index[1])
+            ? ($nums3[$index[0]] + $nums3[$index[1]]) / 2
+            : $nums3[$index[0]];
+    }
+}
diff --git a/src/main/php/g0001_0100/s0004_median_of_two_sorted_arrays/readme.md b/src/main/php/g0001_0100/s0004_median_of_two_sorted_arrays/readme.md
new file mode 100644
index 0000000..a463374
--- /dev/null
+++ b/src/main/php/g0001_0100/s0004_median_of_two_sorted_arrays/readme.md
@@ -0,0 +1,50 @@
+4\. Median of Two Sorted Arrays
+
+Hard
+
+Given two sorted arrays `nums1` and `nums2` of size `m` and `n` respectively, return **the median** of the two sorted arrays.
+
+The overall run time complexity should be `O(log (m+n))`.
+
+**Example 1:**
+
+**Input:** nums1 = [1,3], nums2 = [2]
+
+**Output:** 2.00000
+
+**Explanation:** merged array = [1,2,3] and median is 2. 
+
+**Example 2:**
+
+**Input:** nums1 = [1,2], nums2 = [3,4]
+
+**Output:** 2.50000
+
+**Explanation:** merged array = [1,2,3,4] and median is (2 + 3) / 2 = 2.5. 
+
+**Example 3:**
+
+**Input:** nums1 = [0,0], nums2 = [0,0]
+
+**Output:** 0.00000 
+
+**Example 4:**
+
+**Input:** nums1 = [], nums2 = [1]
+
+**Output:** 1.00000 
+
+**Example 5:**
+
+**Input:** nums1 = [2], nums2 = []
+
+**Output:** 2.00000 
+
+**Constraints:**
+
+*   `nums1.length == m`
+*   `nums2.length == n`
+*   `0 <= m <= 1000`
+*   `0 <= n <= 1000`
+*   `1 <= m + n <= 2000`
+*   <code>-10<sup>6</sup> <= nums1[i], nums2[i] <= 10<sup>6</sup></code>
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0005_longest_palindromic_substring/Solution.php b/src/main/php/g0001_0100/s0005_longest_palindromic_substring/Solution.php
new file mode 100644
index 0000000..870b3b9
--- /dev/null
+++ b/src/main/php/g0001_0100/s0005_longest_palindromic_substring/Solution.php
@@ -0,0 +1,42 @@
+<?php
+
+namespace leetcode\g0001_0100\s0005_longest_palindromic_substring;
+
+// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #String #Dynamic_Programming
+// #Data_Structure_II_Day_9_String #Algorithm_II_Day_14_Dynamic_Programming
+// #Dynamic_Programming_I_Day_17 #Udemy_Strings #Big_O_Time_O(n)_Space_O(n)
+// #2023_12_03_Time_13_ms_(98.57%)_Space_19.4_MB_(12.54%)
+
+class Solution {
+    /**
+     * @param String $s
+     * @return String
+     */
+    function longestPalindrome($s): string {
+        if (($length = strlen($s)) <= 1) {
+            return $s;
+        }
+        if (strrev($s) === $s) {
+            return $s;
+        }
+
+        $max_length = 1;
+        for ($i = 0; $i < $length; ++$i) {
+            for ($len = $max_length; $len <= $length; ++$len) {
+                $start = $i - ($len >> 1);
+                if ($start < 0 || $start + $len > $length) {
+                    break;
+                }
+                $substr = substr($s, $start, $len);
+                if ($substr === strrev($substr)) {
+                    $str = $substr;
+                    $max_length = $len;
+                } elseif ($max_length + 1 < $len) {
+                    break;
+                }
+            }
+        }
+
+        return $str;
+    }
+}
diff --git a/src/main/php/g0001_0100/s0005_longest_palindromic_substring/readme.md b/src/main/php/g0001_0100/s0005_longest_palindromic_substring/readme.md
new file mode 100644
index 0000000..883ff5c
--- /dev/null
+++ b/src/main/php/g0001_0100/s0005_longest_palindromic_substring/readme.md
@@ -0,0 +1,34 @@
+5\. Longest Palindromic Substring
+
+Medium
+
+Given a string `s`, return _the longest palindromic substring_ in `s`.
+
+**Example 1:**
+
+**Input:** s = "babad"
+
+**Output:** "bab" **Note:** "aba" is also a valid answer. 
+
+**Example 2:**
+
+**Input:** s = "cbbd"
+
+**Output:** "bb" 
+
+**Example 3:**
+
+**Input:** s = "a"
+
+**Output:** "a" 
+
+**Example 4:**
+
+**Input:** s = "ac"
+
+**Output:** "a" 
+
+**Constraints:**
+
+*   `1 <= s.length <= 1000`
+*   `s` consist of only digits and English letters.
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0006_zigzag_conversion/Solution.php b/src/main/php/g0001_0100/s0006_zigzag_conversion/Solution.php
new file mode 100644
index 0000000..754f890
--- /dev/null
+++ b/src/main/php/g0001_0100/s0006_zigzag_conversion/Solution.php
@@ -0,0 +1,38 @@
+<?php
+
+namespace leetcode\g0001_0100\s0006_zigzag_conversion;
+
+// #Medium #String #2023_12_03_Time_12_ms_(80.63%)_Space_19.3_MB_(57.66%)
+
+class Solution {
+    /**
+     * @param String $s
+     * @param Integer $numRows
+     * @return String
+     */
+    function convert($s, $numRows) {
+        if ($numRows == 1) {
+            return $s;
+        }
+        $row = 0;
+        $col = 0;
+        $dir = 'down';
+        for ($i = 0; $i < strlen($s); $i++) {
+            $string[$row][] = $s[$i];
+            if ($row < $numRows - 1 && $dir == 'down') {
+                $row++;
+            } elseif ($row == $numRows - 1 && $dir == 'down') {
+                $row--;
+                $dir = 'up';
+                $col++;
+            } elseif ($row > 0) {
+                $row--;
+                $col++;
+            } else {
+                $dir = 'down';
+                $row++;
+            }
+        }
+        return implode(array_merge(...$string));
+    }
+}
diff --git a/src/main/php/g0001_0100/s0006_zigzag_conversion/readme.md b/src/main/php/g0001_0100/s0006_zigzag_conversion/readme.md
new file mode 100644
index 0000000..4f55d57
--- /dev/null
+++ b/src/main/php/g0001_0100/s0006_zigzag_conversion/readme.md
@@ -0,0 +1,39 @@
+6\. Zigzag Conversion
+
+Medium
+
+The string `"PAYPALISHIRING"` is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)
+
+P A H N A P L S I I G Y I R 
+
+And then read line by line: `"PAHNAPLSIIGYIR"`
+
+Write the code that will take a string and make this conversion given a number of rows:
+
+string convert(string s, int numRows); 
+
+**Example 1:**
+
+**Input:** s = "PAYPALISHIRING", numRows = 3
+
+**Output:** "PAHNAPLSIIGYIR" 
+
+**Example 2:**
+
+**Input:** s = "PAYPALISHIRING", numRows = 4
+
+**Output:** "PINALSIGYAHRPI"
+
+**Explanation:** P I N A L S I G Y A H R P I 
+
+**Example 3:**
+
+**Input:** s = "A", numRows = 1
+
+**Output:** "A" 
+
+**Constraints:**
+
+*   `1 <= s.length <= 1000`
+*   `s` consists of English letters (lower-case and upper-case), `','` and `'.'`.
+*   `1 <= numRows <= 1000`
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0007_reverse_integer/Solution.php b/src/main/php/g0001_0100/s0007_reverse_integer/Solution.php
new file mode 100644
index 0000000..b98420e
--- /dev/null
+++ b/src/main/php/g0001_0100/s0007_reverse_integer/Solution.php
@@ -0,0 +1,23 @@
+<?php
+
+namespace leetcode\g0001_0100\s0007_reverse_integer;
+
+// #Medium #Top_Interview_Questions #Math #Udemy_Integers
+// #2023_12_03_Time_3_ms_(90.99%)_Space_19.2_MB_(44.23%)
+
+class Solution {
+    function reverse($x) {
+        $ls_negative = '';
+        if (strpos($x, '-') === 0) {
+            $ls_negative = substr($x, 0, 1);
+            $x = substr($x, 1);
+        }
+        $la_chars = str_split($x);
+        $la_chars = array_reverse($la_chars);
+        $li_result = intval($ls_negative . implode('', $la_chars));
+        if ($li_result > 2147483647 || $li_result < -2147483647) {
+            $li_result = 0;
+        }
+        return $li_result;
+    }
+}
diff --git a/src/main/php/g0001_0100/s0007_reverse_integer/readme.md b/src/main/php/g0001_0100/s0007_reverse_integer/readme.md
new file mode 100644
index 0000000..81dbb62
--- /dev/null
+++ b/src/main/php/g0001_0100/s0007_reverse_integer/readme.md
@@ -0,0 +1,35 @@
+7\. Reverse Integer
+
+Medium
+
+Given a signed 32-bit integer `x`, return `x` _with its digits reversed_. If reversing `x` causes the value to go outside the signed 32-bit integer range <code>[-2<sup>31</sup>, 2<sup>31</sup> - 1]</code>, then return `0`.
+
+**Assume the environment does not allow you to store 64-bit integers (signed or unsigned).**
+
+**Example 1:**
+
+**Input:** x = 123
+
+**Output:** 321 
+
+**Example 2:**
+
+**Input:** x = -123
+
+**Output:** -321 
+
+**Example 3:**
+
+**Input:** x = 120
+
+**Output:** 21 
+
+**Example 4:**
+
+**Input:** x = 0
+
+**Output:** 0 
+
+**Constraints:**
+
+*   <code>-2<sup>31</sup> <= x <= 2<sup>31</sup> - 1</code>
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0008_string_to_integer_atoi/Solution.php b/src/main/php/g0001_0100/s0008_string_to_integer_atoi/Solution.php
new file mode 100644
index 0000000..9804c2b
--- /dev/null
+++ b/src/main/php/g0001_0100/s0008_string_to_integer_atoi/Solution.php
@@ -0,0 +1,44 @@
+<?php
+
+namespace leetcode\g0001_0100\s0008_string_to_integer_atoi;
+
+// #Medium #Top_Interview_Questions #String #2023_12_03_Time_3_ms_(93.18%)_Space_19.1_MB_(36.36%)
+
+class Solution {
+    /**
+     * @param String $s
+     * @return Integer
+     */
+    function myAtoi($s) {
+        $pos = 0;
+        $res = 0;
+        for ($i = 0; $i < strlen($s); $i++) {
+            if (ctype_digit($s[$i])) {
+                if ($res == 0 && $pos == 0) {
+                    $pos++;
+                }
+                $res = $pos * (abs($res * 10) + $s[$i]);
+                if ($res >= 2147483647) {
+                    return 2147483647;
+                }
+                if ($res <= -2147483648) {
+                    return -2147483648;
+                }
+            } else {
+                if ($s[$i] == ' ' && $pos == 0) {
+                    continue;
+                }
+                if ($s[$i] == '-' && $pos == 0) {
+                    $pos--;
+                    continue;
+                }
+                if ($s[$i] == '+' && $pos == 0) {
+                    $pos++;
+                    continue;
+                }
+                break;
+            }
+        }
+        return $res;
+    }
+}
diff --git a/src/main/php/g0001_0100/s0008_string_to_integer_atoi/readme.md b/src/main/php/g0001_0100/s0008_string_to_integer_atoi/readme.md
new file mode 100644
index 0000000..af67f64
--- /dev/null
+++ b/src/main/php/g0001_0100/s0008_string_to_integer_atoi/readme.md
@@ -0,0 +1,113 @@
+8\. String to Integer (atoi)
+
+Medium
+
+Implement the `myAtoi(string s)` function, which converts a string to a 32-bit signed integer (similar to C/C++'s `atoi` function).
+
+The algorithm for `myAtoi(string s)` is as follows:
+
+1.  Read in and ignore any leading whitespace.
+2.  Check if the next character (if not already at the end of the string) is `'-'` or `'+'`. Read this character in if it is either. This determines if the final result is negative or positive respectively. Assume the result is positive if neither is present.
+3.  Read in next the characters until the next non-digit character or the end of the input is reached. The rest of the string is ignored.
+4.  Convert these digits into an integer (i.e. `"123" -> 123`, `"0032" -> 32`). If no digits were read, then the integer is `0`. Change the sign as necessary (from step 2).
+5.  If the integer is out of the 32-bit signed integer range <code>[-2<sup>31</sup>, 2<sup>31</sup> - 1]</code>, then clamp the integer so that it remains in the range. Specifically, integers less than <code>-2<sup>31</sup></code> should be clamped to <code>-2<sup>31</sup></code>, and integers greater than <code>2<sup>31</sup> - 1</code> should be clamped to <code>2<sup>31</sup> - 1</code>.
+6.  Return the integer as the final result.
+
+**Note:**
+
+*   Only the space character `' '` is considered a whitespace character.
+*   **Do not ignore** any characters other than the leading whitespace or the rest of the string after the digits.
+
+**Example 1:**
+
+**Input:** s = "42"
+
+**Output:** 42
+
+**Explanation:** The underlined characters are what is read in, the caret is the current reader position.
+
+    Step 1: "42" (no characters read because there is no leading whitespace)
+             ^ 
+    Step 2: "42" (no characters read because there is neither a '-' nor '+')
+             ^
+    Step 3: "42" ("42" is read in)
+               ^
+
+The parsed integer is 42. Since 42 is in the range [-2<sup>31</sup>, 2<sup>31</sup> - 1], the final result is 42. 
+
+**Example 2:**
+
+**Input:** s = " -42"
+
+**Output:** -42
+
+**Explanation:**
+
+    Step 1: " -42" (leading whitespace is read and ignored)
+              ^ 
+    Step 2: " -42" ('-' is read, so the result should be negative)
+               ^
+    Step 3: " -42" ("42" is read in)
+                 ^
+    The parsed integer is -42.
+
+Since -42 is in the range [-2<sup>31</sup>, 2<sup>31</sup> - 1], the final result is -42. 
+
+**Example 3:**
+
+**Input:** s = "4193 with words"
+
+**Output:** 4193
+
+**Explanation:**
+
+    Step 1: "4193 with words" (no characters read because there is no leading whitespace)
+             ^
+    Step 2: "4193 with words" (no characters read because there is neither a '-' nor '+')
+             ^
+    Step 3: "4193 with words" ("4193" is read in; reading stops because the next character is a non-digit)
+                 ^ 
+    The parsed integer is 4193.
+
+Since 4193 is in the range [-2<sup>31</sup>, 2<sup>31</sup> - 1], the final result is 4193. 
+
+**Example 4:**
+
+**Input:** s = "words and 987"
+
+**Output:** 0
+
+**Explanation:**
+
+    Step 1: "words and 987" (no characters read because there is no leading whitespace)
+             ^
+    Step 2: "words and 987" (no characters read because there is neither a '-' nor '+')
+             ^
+    Step 3: "words and 987" (reading stops immediately because there is a non-digit 'w')
+             ^
+    The parsed integer is 0 because no digits were read.
+
+Since 0 is in the range [-2<sup>31</sup>, 2<sup>31</sup> - 1], the final result is 0. 
+
+**Example 5:**
+
+**Input:** s = "-91283472332"
+
+**Output:** -2147483648
+
+**Explanation:**
+
+    Step 1: "-91283472332" (no characters read because there is no leading whitespace)
+            ^
+    Step 2: "-91283472332" ('-' is read, so the result should be negative)
+              ^
+    Step 3: "-91283472332" ("91283472332" is read in)
+                         ^
+    The parsed integer is -91283472332.
+
+Since -91283472332 is less than the lower bound of the range [-2<sup>31</sup>, 2<sup>31</sup> - 1], the final result is clamped to -2<sup>31</sup> = -2147483648.  
+
+**Constraints:**
+
+*   `0 <= s.length <= 200`
+*   `s` consists of English letters (lower-case and upper-case), digits (`0-9`), `' '`, `'+'`, `'-'`, and `'.'`.
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0009_palindrome_number/Solution.php b/src/main/php/g0001_0100/s0009_palindrome_number/Solution.php
new file mode 100644
index 0000000..bf49357
--- /dev/null
+++ b/src/main/php/g0001_0100/s0009_palindrome_number/Solution.php
@@ -0,0 +1,39 @@
+<?php
+
+namespace leetcode\g0001_0100\s0009_palindrome_number;
+
+// #Easy #Math #Udemy_Integers #2023_12_03_Time_23_ms_(76.73%)_Space_19.4_MB_(5.93%)
+
+class Solution {
+    /**
+     * @param Integer $x
+     * @return Boolean
+     */
+    function isPalindrome($x) {
+        if ($x < 0) {
+            return false;
+        }
+        $x = (string)$x;
+        $size = strlen($x);
+        if ($size % 2 == 1) {
+            $c = ($size - 1) / 2;
+            for ($i = 0; $i < $c; $i++) {
+                if ($i == $c) {
+                    return true;
+                }
+                if ($x[$i] !== $x[$size - ($i + 1)]) {
+                    return false;
+                }
+            }
+            return true;
+        } else {
+            $c = $size / 2;
+            for ($i = 0; $i < $c; $i++) {
+                if ($x[$i] !== $x[$size - ($i + 1)]) {
+                    return false;
+                }
+            }
+            return true;
+        }
+    }
+}
diff --git a/src/main/php/g0001_0100/s0009_palindrome_number/readme.md b/src/main/php/g0001_0100/s0009_palindrome_number/readme.md
new file mode 100644
index 0000000..f05939b
--- /dev/null
+++ b/src/main/php/g0001_0100/s0009_palindrome_number/readme.md
@@ -0,0 +1,41 @@
+9\. Palindrome Number
+
+Easy
+
+Given an integer `x`, return `true` if `x` is palindrome integer.
+
+An integer is a **palindrome** when it reads the same backward as forward. For example, `121` is palindrome while `123` is not.
+
+**Example 1:**
+
+**Input:** x = 121
+
+**Output:** true 
+
+**Example 2:**
+
+**Input:** x = -121
+
+**Output:** false
+
+**Explanation:** From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome. 
+
+**Example 3:**
+
+**Input:** x = 10
+
+**Output:** false
+
+**Explanation:** Reads 01 from right to left. Therefore it is not a palindrome. 
+
+**Example 4:**
+
+**Input:** x = -101
+
+**Output:** false 
+
+**Constraints:**
+
+*   <code>-2<sup>31</sup> <= x <= 2<sup>31</sup> - 1</code>
+
+**Follow up:** Could you solve it without converting the integer to a string?
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0010_regular_expression_matching/Solution.php b/src/main/php/g0001_0100/s0010_regular_expression_matching/Solution.php
new file mode 100644
index 0000000..1509038
--- /dev/null
+++ b/src/main/php/g0001_0100/s0010_regular_expression_matching/Solution.php
@@ -0,0 +1,39 @@
+<?php
+
+namespace leetcode\g0001_0100\s0010_regular_expression_matching;
+
+// #Hard #Top_100_Liked_Questions #Top_Interview_Questions #String #Dynamic_Programming #Recursion
+// #Udemy_Dynamic_Programming #Big_O_Time_O(m*n)_Space_O(m*n)
+// #2023_12_03_Time_10_ms_(64.52%)_Space_19.3_MB_(61.29%)
+
+class Solution {
+    private $cache;
+
+    /**
+     * @param String $s
+     * @param String $p
+     * @return Boolean
+     */
+    public function isMatch($s, $p) {
+        $this->cache = array_fill(0, strlen($s) + 1, array_fill(0, strlen($p) + 1, null));
+        return $this->isMatchHelper($s, $p, 0, 0);
+    }
+
+    private function isMatchHelper($s, $p, $i, $j) {
+        if ($j == strlen($p)) {
+            return $i == strlen($s);
+        }
+        if ($this->cache[$i][$j] !== null) {
+            return $this->cache[$i][$j];
+        }
+        $firstMatch = ($i < strlen($s)) && ($s[$i] == $p[$j] || $p[$j] == '.');
+        if (($j + 1) < strlen($p) && $p[$j + 1] == '*') {
+            $result = ($firstMatch && $this->isMatchHelper($s, $p, $i + 1, $j)) ||
+                $this->isMatchHelper($s, $p, $i, $j + 2);
+        } else {
+            $result = $firstMatch && $this->isMatchHelper($s, $p, $i + 1, $j + 1);
+        }
+        $this->cache[$i][$j] = $result;
+        return $result;
+    }
+}
diff --git a/src/main/php/g0001_0100/s0010_regular_expression_matching/readme.md b/src/main/php/g0001_0100/s0010_regular_expression_matching/readme.md
new file mode 100644
index 0000000..f614e74
--- /dev/null
+++ b/src/main/php/g0001_0100/s0010_regular_expression_matching/readme.md
@@ -0,0 +1,56 @@
+10\. Regular Expression Matching
+
+Hard
+
+Given an input string `s` and a pattern `p`, implement regular expression matching with support for `'.'` and `'*'` where:
+
+*   `'.'` Matches any single character.
+*   `'*'` Matches zero or more of the preceding element.
+
+The matching should cover the **entire** input string (not partial).
+
+**Example 1:**
+
+**Input:** s = "aa", p = "a"
+
+**Output:** false
+
+**Explanation:** "a" does not match the entire string "aa". 
+
+**Example 2:**
+
+**Input:** s = "aa", p = "a\*"
+
+**Output:** true
+
+**Explanation:** '\*' means zero or more of the preceding element, 'a'. Therefore, by repeating 'a' once, it becomes "aa". 
+
+**Example 3:**
+
+**Input:** s = "ab", p = ".\*"
+
+**Output:** true
+
+**Explanation:** ".\*" means "zero or more (\*) of any character (.)". 
+
+**Example 4:**
+
+**Input:** s = "aab", p = "c\*a\*b"
+
+**Output:** true
+
+**Explanation:** c can be repeated 0 times, a can be repeated 1 time. Therefore, it matches "aab". 
+
+**Example 5:**
+
+**Input:** s = "mississippi", p = "mis\*is\*p\*."
+
+**Output:** false 
+
+**Constraints:**
+
+*   `1 <= s.length <= 20`
+*   `1 <= p.length <= 30`
+*   `s` contains only lowercase English letters.
+*   `p` contains only lowercase English letters, `'.'`, and `'*'`.
+*   It is guaranteed for each appearance of the character `'*'`, there will be a previous valid character to match.
\ No newline at end of file
diff --git a/src/test/php/g0001_0100/s0003_longest_substring_without_repeating_characters/SolutionTest.php b/src/test/php/g0001_0100/s0003_longest_substring_without_repeating_characters/SolutionTest.php
new file mode 100644
index 0000000..26214aa
--- /dev/null
+++ b/src/test/php/g0001_0100/s0003_longest_substring_without_repeating_characters/SolutionTest.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace leetcode\g0001_0100\s0003_longest_substring_without_repeating_characters;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testLengthOfLongestSubstring() {
+        $this->assertEquals(3, (new Solution())->lengthOfLongestSubstring("abcabcbb"));
+    }
+
+    public function testLengthOfLongestSubstring2() {
+        $this->assertEquals(1, (new Solution())->lengthOfLongestSubstring("bbbbb"));
+    }
+
+    public function testLengthOfLongestSubstring3() {
+        $this->assertEquals(3, (new Solution())->lengthOfLongestSubstring("pwwkew"));
+    }
+}
diff --git a/src/test/php/g0001_0100/s0004_median_of_two_sorted_arrays/SolutionTest.php b/src/test/php/g0001_0100/s0004_median_of_two_sorted_arrays/SolutionTest.php
new file mode 100644
index 0000000..178a010
--- /dev/null
+++ b/src/test/php/g0001_0100/s0004_median_of_two_sorted_arrays/SolutionTest.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace leetcode\g0001_0100\s0004_median_of_two_sorted_arrays;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testFindMedianSortedArrays() {
+        $this->assertEquals(2.0, (new Solution())->findMedianSortedArrays([1, 3], [2]));
+    }
+
+    public function testFindMedianSortedArrays2() {
+        $this->assertEquals(2.5, (new Solution())->findMedianSortedArrays([1, 2], [3, 4]));
+    }
+}
diff --git a/src/test/php/g0001_0100/s0005_longest_palindromic_substring/SolutionTest.php b/src/test/php/g0001_0100/s0005_longest_palindromic_substring/SolutionTest.php
new file mode 100644
index 0000000..dc0baee
--- /dev/null
+++ b/src/test/php/g0001_0100/s0005_longest_palindromic_substring/SolutionTest.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace leetcode\g0001_0100\s0005_longest_palindromic_substring;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testLongestPalindrome() {
+        $this->assertEquals("aba", (new Solution())->longestPalindrome("babad"));
+    }
+
+    public function testLongestPalindrome2() {
+        $this->assertEquals("bb", (new Solution())->longestPalindrome("cbbd"));
+    }
+}
diff --git a/src/test/php/g0001_0100/s0006_zigzag_conversion/SolutionTest.php b/src/test/php/g0001_0100/s0006_zigzag_conversion/SolutionTest.php
new file mode 100644
index 0000000..2a91119
--- /dev/null
+++ b/src/test/php/g0001_0100/s0006_zigzag_conversion/SolutionTest.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace leetcode\g0001_0100\s0006_zigzag_conversion;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testConvert() {
+        $this->assertEquals("PAHNAPLSIIGYIR", (new Solution())->convert("PAYPALISHIRING", 3));
+    }
+
+    public function testConvert2() {
+        $this->assertEquals("PINALSIGYAHRPI", (new Solution())->convert("PAYPALISHIRING", 4));
+    }
+}
diff --git a/src/test/php/g0001_0100/s0007_reverse_integer/SolutionTest.php b/src/test/php/g0001_0100/s0007_reverse_integer/SolutionTest.php
new file mode 100644
index 0000000..21e2cc4
--- /dev/null
+++ b/src/test/php/g0001_0100/s0007_reverse_integer/SolutionTest.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace leetcode\g0001_0100\s0007_reverse_integer;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testReverse() {
+        $this->assertEquals(321, (new Solution())->reverse(123));
+    }
+
+    public function testReverse2() {
+        $this->assertEquals(-321, (new Solution())->reverse(-123));
+    }
+
+    public function testReverse3() {
+        $this->assertEquals(21, (new Solution())->reverse(120));
+    }
+}
diff --git a/src/test/php/g0001_0100/s0008_string_to_integer_atoi/SolutionTest.php b/src/test/php/g0001_0100/s0008_string_to_integer_atoi/SolutionTest.php
new file mode 100644
index 0000000..db8873b
--- /dev/null
+++ b/src/test/php/g0001_0100/s0008_string_to_integer_atoi/SolutionTest.php
@@ -0,0 +1,27 @@
+<?php
+
+namespace leetcode\g0001_0100\s0008_string_to_integer_atoi;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testMyAtoi() {
+        $this->assertEquals(42, (new Solution())->myAtoi("42"));
+    }
+
+    public function testMyAtoi2() {
+        $this->assertEquals(-42, (new Solution())->myAtoi("   -42"));
+    }
+
+    public function testMyAtoi3() {
+        $this->assertEquals(4193, (new Solution())->myAtoi("4193 with words"));
+    }
+
+    public function testMyAtoi4() {
+        $this->assertEquals(0, (new Solution())->myAtoi("words and 987"));
+    }
+
+    public function testMyAtoi5() {
+        $this->assertEquals(-2147483648, (new Solution())->myAtoi("-91283472332"));
+    }
+}
diff --git a/src/test/php/g0001_0100/s0009_palindrome_number/SolutionTest.php b/src/test/php/g0001_0100/s0009_palindrome_number/SolutionTest.php
new file mode 100644
index 0000000..25cfca0
--- /dev/null
+++ b/src/test/php/g0001_0100/s0009_palindrome_number/SolutionTest.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace leetcode\g0001_0100\s0009_palindrome_number;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testIsPalindrome() {
+        $this->assertTrue((new Solution())->isPalindrome(121));
+    }
+
+    public function testIsPalindrome2() {
+        $this->assertFalse((new Solution())->isPalindrome(-121));
+    }
+
+    public function testIsPalindrome3() {
+        $this->assertFalse((new Solution())->isPalindrome(10));
+    }
+}
diff --git a/src/test/php/g0001_0100/s0010_regular_expression_matching/SolutionTest.php b/src/test/php/g0001_0100/s0010_regular_expression_matching/SolutionTest.php
new file mode 100644
index 0000000..b84a1e2
--- /dev/null
+++ b/src/test/php/g0001_0100/s0010_regular_expression_matching/SolutionTest.php
@@ -0,0 +1,27 @@
+<?php
+
+namespace leetcode\g0001_0100\s0010_regular_expression_matching;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testIsMatch() {
+        $this->assertFalse((new Solution())->isMatch("aa", "a"));
+    }
+
+    public function testIsMatch2() {
+        $this->assertTrue((new Solution())->isMatch("aa", "a*"));
+    }
+
+    public function testIsMatch3() {
+        $this->assertTrue((new Solution())->isMatch("ab", ".*"));
+    }
+
+    public function testIsMatch4() {
+        $this->assertTrue((new Solution())->isMatch("aab", "c*a*b"));
+    }
+
+    public function testIsMatch5() {
+        $this->assertFalse((new Solution())->isMatch("mississippi", "mis*is*p*."));
+    }
+}