Added racket

src/main/racket/g0001_0100/s0001_two_sum/Solution.rkt

@@ -1,6 +1,7 @@
 ; #Easy #Top_100_Liked_Questions #Top_Interview_Questions #Array #Hash_Table
-; #Data_Structure_I_Day_2_Array #Level_1_Day_13_Hashmap #Udemy_Arrays #Big_O_Time_O(n)_Space_O(n)
-; #AI_can_be_used_to_solve_the_task #2025_01_28_Time_0_(100.00%)_Space_102.07_(45.83%)
+; #Data_Structure_I_Day_2_Array #Level_1_Day_13_Hashmap #Udemy_Arrays #Top_Interview_150_Hashmap
+; #Big_O_Time_O(n)_Space_O(n) #AI_can_be_used_to_solve_the_task
+; #2025_02_05_Time_0_(100.00%)_Space_102.04_(40.82%)
 
 (define (two-sum-iter nums target hash index)
   (cond

src/main/racket/g0001_0100/s0002_add_two_numbers/Solution.rkt

@@ -1,7 +1,7 @@
 ; #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Math #Linked_List #Recursion
 ; #Data_Structure_II_Day_10_Linked_List #Programming_Skills_II_Day_15
-; #Big_O_Time_O(max(N,M))_Space_O(max(N,M)) #AI_can_be_used_to_solve_the_task
-; #2025_01_28_Time_0_(100.00%)_Space_128.42_(12.50%)
+; #Top_Interview_150_Linked_List #Big_O_Time_O(max(N,M))_Space_O(max(N,M))
+; #AI_can_be_used_to_solve_the_task #2025_02_05_Time_0_(100.00%)_Space_128.08_(72.73%)
 
 ; Definition for singly-linked list:
 #|

src/main/racket/g0001_0100/s0003_longest_substring_without_repeating_characters/Solution.rkt

@@ -1,7 +1,7 @@
 ; #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) #AI_can_be_used_to_solve_the_task
-; #2025_01_28_Time_134_(75.00%)_Space_132.36_(100.00%)
+; #Top_Interview_150_Sliding_Window #Big_O_Time_O(n)_Space_O(1) #AI_can_be_used_to_solve_the_task
+; #2025_02_06_Time_119_(71.43%)_Space_131.37_(28.57%)
 
 ; Helper function to get the sublist up to 'v' excluded.
 (define (take-till q v)

src/main/racket/g0001_0100/s0004_median_of_two_sorted_arrays/Solution.rkt

@@ -1,6 +1,6 @@
 ; #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) #AI_can_be_used_to_solve_the_task
-; #2025_01_28_Time_0_(100.00%)_Space_128.57_(100.00%)
+; #Top_Interview_150_Binary_Search #Big_O_Time_O(log(min(N,M)))_Space_O(1)
+; #AI_can_be_used_to_solve_the_task #2025_02_06_Time_0_(100.00%)_Space_128.80_(25.00%)
 
 (define/contract (find-median-sorted-arrays nums1 nums2)
   (-> (listof exact-integer?) (listof exact-integer?) flonum?)

src/main/racket/g0001_0100/s0005_longest_palindromic_substring/Solution.rkt

@@ -1,7 +1,7 @@
 ; #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)
-; #2025_01_28_Time_10_(50.00%)_Space_102.35_(50.00%)
+; #Dynamic_Programming_I_Day_17 #Udemy_Strings #Top_Interview_150_Multidimensional_DP
+; #Big_O_Time_O(n)_Space_O(n) #2025_02_06_Time_4_(100.00%)_Space_101.40_(85.71%)
 
 (define (longest-palindrome s)
   (define (expand-around-center s left right)

src/main/racket/g0001_0100/s0064_minimum_path_sum/Solution.rkt

@@ -0,0 +1,53 @@
+; #Medium #Top_100_Liked_Questions #Array #Dynamic_Programming #Matrix
+; #Dynamic_Programming_I_Day_16 #Udemy_Dynamic_Programming #Top_Interview_150_Multidimensional_DP
+; #Big_O_Time_O(m*n)_Space_O(m*n) #2025_02_04_Time_92_(100.00%)_Space_133.91_(100.00%)
+
+; dynamic programming helper function
+(define (mpsAux grid curpos dpTable ub)
+	(local
+		[(define (get grid pos) (list-ref (list-ref grid (car pos)) (cdr pos)))]
+		(cond
+			; return start value
+			[(equal? curpos (cons 0 0)) (car (car grid))]
+
+			; handle out of bounds
+			[(or (< (car curpos) 0) (< (cdr curpos) 0)) +inf.0]
+
+			; position appeared before
+			[(hash-ref dpTable curpos #f) (hash-ref dpTable curpos)]
+
+			; inductive case
+			[else
+				(let*
+					(
+						; go up
+						[u_val (mpsAux grid (cons (- (car curpos) 1) (cdr curpos)) dpTable ub)]
+
+						; go left 
+						[l_val (mpsAux grid (cons (car curpos) (- (cdr curpos) 1)) dpTable ub)]
+
+						; compute the current least cost
+						[cur-least-cost (+ (get grid curpos) (min u_val l_val))]
+					)
+					(hash-set! dpTable curpos cur-least-cost)
+					cur-least-cost
+				)
+			]
+		)
+	)
+)
+
+; the (x . y) position of the grid is the x'th row and y'th column of the grid
+(define/contract (min-path-sum grid)
+	(-> (listof (listof exact-integer?)) exact-integer?)
+	(local
+		[(define dpTable (make-hash))]
+		(let*
+			(
+				[curpos (cons (- (length grid) 1) (- (length (car grid)) 1))]
+				[least-val (mpsAux grid curpos dpTable 200)]
+			)
+			(inexact->exact least-val)
+		)
+	)
+)

src/main/racket/g0001_0100/s0064_minimum_path_sum/readme.md

@@ -0,0 +1,30 @@
+64\. Minimum Path Sum
+
+Medium
+
+Given a `m x n` `grid` filled with non-negative numbers, find a path from top left to bottom right, which minimizes the sum of all numbers along its path.
+
+**Note:** You can only move either down or right at any point in time.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2020/11/05/minpath.jpg)
+
+**Input:** grid = [[1,3,1],[1,5,1],[4,2,1]]
+
+**Output:** 7
+
+**Explanation:** Because the path 1 → 3 → 1 → 1 → 1 minimizes the sum.
+
+**Example 2:**
+
+**Input:** grid = [[1,2,3],[4,5,6]]
+
+**Output:** 12
+
+**Constraints:**
+
+*   `m == grid.length`
+*   `n == grid[i].length`
+*   `1 <= m, n <= 200`
+*   `0 <= grid[i][j] <= 100`

src/main/racket/g0001_0100/s0070_climbing_stairs/Solution.rkt

@@ -0,0 +1,40 @@
+; #Easy #Top_100_Liked_Questions #Top_Interview_Questions #Dynamic_Programming #Math #Memoization
+; #Algorithm_I_Day_12_Dynamic_Programming #Dynamic_Programming_I_Day_2
+; #Level_1_Day_10_Dynamic_Programming #Udemy_Dynamic_Programming #Top_Interview_150_1D_DP
+; #Big_O_Time_O(n)_Space_O(n) #2025_02_04_Time_0_(100.00%)_Space_101.51_(100.00%)
+
+(define (clmHelp n hTable)
+	(cond
+		; base cases
+		((= 1 n) 1)
+		((= 2 n) 2)
+		((hash-ref hTable n #f) (hash-ref hTable n))
+
+		; inductive case
+		(else
+			(let*
+				; the local variables
+				(
+					(a (clmHelp (- n 1) hTable))
+					(b (clmHelp (- n 2) hTable))
+					(numPos (+ a b))
+				)
+
+				; the body
+				(hash-set! hTable n numPos)
+				numPos
+			)
+		)
+	)
+)
+
+(define/contract (climb-stairs n)
+	(-> exact-integer? exact-integer?)
+	(local
+		; local definitions
+		((define hTable (make-hash)))
+
+		; function body
+		(clmHelp n hTable)
+	)
+)

src/main/racket/g0001_0100/s0070_climbing_stairs/readme.md

@@ -0,0 +1,37 @@
+70\. Climbing Stairs
+
+Easy
+
+You are climbing a staircase. It takes `n` steps to reach the top.
+
+Each time you can either climb `1` or `2` steps. In how many distinct ways can you climb to the top?
+
+**Example 1:**
+
+**Input:** n = 2
+
+**Output:** 2
+
+**Explanation:** There are two ways to climb to the top. 
+
+1. 1 step + 1 step 
+
+2. 2 steps
+
+**Example 2:**
+
+**Input:** n = 3
+
+**Output:** 3
+
+**Explanation:** There are three ways to climb to the top. 
+
+1. 1 step + 1 step + 1 step 
+
+2. 1 step + 2 steps 
+
+3. 2 steps + 1 step
+
+**Constraints:**
+
+*   `1 <= n <= 45`

src/main/racket/g0001_0100/s0072_edit_distance/Solution.rkt

@@ -0,0 +1,25 @@
+; #Medium #Top_100_Liked_Questions #String #Dynamic_Programming
+; #Algorithm_II_Day_18_Dynamic_Programming #Dynamic_Programming_I_Day_19
+; #Udemy_Dynamic_Programming #Top_Interview_150_Multidimensional_DP #Big_O_Time_O(n^2)_Space_O(n2)
+; #2025_02_04_Time_4_(100.00%)_Space_102.31_(100.00%)
+
+(define/contract (min-distance word1 word2)
+  (-> string? string? exact-integer?)
+  (let* ((n1 (string-length word1))
+         (n2 (string-length word2)))
+    (if (> n2 n1)
+        (min-distance word2 word1)
+        (let ((dp (make-vector (+ n2 1) 0)))
+          (for ([j (in-range (+ n2 1))])
+            (vector-set! dp j j))
+          (for ([i (in-range 1 (+ n1 1))])
+            (let ((pre (vector-ref dp 0)))
+              (vector-set! dp 0 i)
+              (for ([j (in-range 1 (+ n2 1))])
+                (let* ((tmp (vector-ref dp j))
+                       (cost (if (char=? (string-ref word1 (- i 1)) (string-ref word2 (- j 1)))
+                                 pre
+                                 (+ 1 (min pre (vector-ref dp j) (vector-ref dp (- j 1)))))))
+                  (vector-set! dp j cost)
+                  (set! pre tmp)))))
+          (vector-ref dp n2)))))

src/main/racket/g0001_0100/s0072_edit_distance/readme.md

@@ -0,0 +1,48 @@
+72\. Edit Distance
+
+Hard
+
+Given two strings `word1` and `word2`, return _the minimum number of operations required to convert `word1` to `word2`_.
+
+You have the following three operations permitted on a word:
+
+*   Insert a character
+*   Delete a character
+*   Replace a character
+
+**Example 1:**
+
+**Input:** word1 = "horse", word2 = "ros"
+
+**Output:** 3
+
+**Explanation:** 
+
+horse -> rorse (replace 'h' with 'r') 
+
+rorse -> rose (remove 'r') 
+
+rose -> ros (remove 'e')
+
+**Example 2:**
+
+**Input:** word1 = "intention", word2 = "execution"
+
+**Output:** 5
+
+**Explanation:** 
+
+intention -> inention (remove 't') 
+
+inention -> enention (replace 'i' with 'e') 
+
+enention -> exention (replace 'n' with 'x') 
+
+exention -> exection (replace 'n' with 'c') 
+
+exection -> execution (insert 'u')
+
+**Constraints:**
+
+*   `0 <= word1.length, word2.length <= 500`
+*   `word1` and `word2` consist of lowercase English letters.

src/main/racket/g0001_0100/s0074_search_a_2d_matrix/Solution.rkt

@@ -0,0 +1,8 @@
+; #Medium #Top_100_Liked_Questions #Array #Binary_Search #Matrix #Data_Structure_I_Day_5_Array
+; #Algorithm_II_Day_1_Binary_Search #Binary_Search_I_Day_8 #Level_2_Day_8_Binary_Search
+; #Udemy_2D_Arrays/Matrix #Top_Interview_150_Binary_Search #Big_O_Time_O(endRow+endCol)_Space_O(1)
+; #2025_02_04_Time_0_(100.00%)_Space_101.20_(100.00%)
+
+(define/contract (search-matrix matrix target)
+  (-> (listof (listof exact-integer?)) exact-integer? boolean?)
+  (not (equal? #f (member target (apply append matrix)))))

src/main/racket/g0001_0100/s0074_search_a_2d_matrix/readme.md

@@ -0,0 +1,31 @@
+74\. Search a 2D Matrix
+
+Medium
+
+Write an efficient algorithm that searches for a value `target` in an `m x n` integer matrix `matrix`. This matrix has the following properties:
+
+*   Integers in each row are sorted from left to right.
+*   The first integer of each row is greater than the last integer of the previous row.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2020/10/05/mat.jpg)
+
+**Input:** matrix = [[1,3,5,7],[10,11,16,20],[23,30,34,60]], target = 3
+
+**Output:** true
+
+**Example 2:**
+
+![](https://assets.leetcode.com/uploads/2020/10/05/mat2.jpg)
+
+**Input:** matrix = [[1,3,5,7],[10,11,16,20],[23,30,34,60]], target = 13
+
+**Output:** false
+
+**Constraints:**
+
+*   `m == matrix.length`
+*   `n == matrix[i].length`
+*   `1 <= m, n <= 100`
+*   <code>-10<sup>4</sup> <= matrix[i][j], target <= 10<sup>4</sup></code>

src/main/racket/g0001_0100/s0076_minimum_window_substring/Solution.rkt

@@ -0,0 +1,66 @@
+; #Hard #Top_100_Liked_Questions #Top_Interview_Questions #String #Hash_Table #Sliding_Window
+; #Level_2_Day_14_Sliding_Window/Two_Pointer #Top_Interview_150_Sliding_Window
+; #Big_O_Time_O(s.length())_Space_O(1) #2025_02_04_Time_151_(100.00%)_Space_130.75_(100.00%)
+
+(define (zip lst1 lst2)
+  (map cons lst1 lst2))
+
+(define (make-zero-hash lst)
+  (make-immutable-hash (zip lst (make-list (length lst) 0))))
+
+(define (hash-inc k ht)
+  (hash-update ht k add1 0))
+
+(define (safe-hash-inc k ht)
+  (if (hash-ref ht k #f) (hash-update ht k add1) ht))
+
+(define (safe-hash-dec k ht)
+  (if (hash-ref ht k #f) (hash-update ht k sub1) ht))
+
+(define (frequencies lst)
+  (foldl hash-inc (hash) lst))
+
+(define (pair-min l1 r1 l2 r2)
+  (if (< (- r1 l1) (- r2 l2)) (values l1 r1) (values l2 r2)))
+
+(define (sref s i) (string-ref s (min (sub1 (string-length s)) i)))
+
+(define (min-window s t)
+  (define t-lst (string->list t))
+
+  (define target (frequencies t-lst))
+
+  (define (delta-dec delta seen c)
+    (cond
+      [(and (hash-ref target c #f) 
+            (< (hash-ref seen c) (hash-ref target c)))
+       (sub1 delta)]
+      [else delta]))
+
+  (define (delta-inc delta seen c)
+    (cond 
+      [(and (hash-ref target c #f)
+            (<= (hash-ref seen c) (hash-ref target c)))
+       (add1 delta)]
+      [else delta]))
+
+  (let loop ([l 0] [r 0] [seen (make-zero-hash t-lst)] 
+             [delta (length t-lst)] [sl 0] [sr 0])
+    (define-values (left-char right-char) (values (sref s l) (sref s r)))
+    (define-values (l* r*) (pair-min l r sl sr))
+    (cond
+      [(and (= 0 sr) 
+            (= delta 0))
+       (loop (add1 l) r (safe-hash-dec left-char seen)
+             (delta-inc delta seen left-char) l r)]
+      [(and (= r (string-length s)) (= delta 0)) 
+       (loop (add1 l) r (safe-hash-dec left-char seen) 
+             (delta-inc delta seen left-char) l* r*)]
+      [(= r (string-length s)) 
+       (substring s sl sr)]
+      [(= delta 0)
+       (loop (add1 l) r (safe-hash-dec left-char seen)
+             (delta-inc delta seen left-char) l* r*)]
+      [else
+       (loop l (add1 r) (safe-hash-inc right-char seen) 
+             (delta-dec delta seen right-char) sl sr)])))