From d05c6952aff9a5c27477625d358626a144a3dcc7 Mon Sep 17 00:00:00 2001
From: coloryourlife <95chris0319@gmail.com>
Date: Sat, 24 Aug 2024 00:37:02 -0700
Subject: [PATCH] coloryourlife: week2 solutions
---
.../coloryourlife.py | 23 +++++++++++++++++
counting-bits/coloryourlife.py | 15 +++++++++++
decode-ways/coloryourlife.py | 23 +++++++++++++++++
encode-and-decode-strings/coloryourlife.py | 25 +++++++++++++++++++
valid-anagram/coloryourlife.py | 18 +++++++++++++
5 files changed, 104 insertions(+)
create mode 100644 construct-binary-tree-from-preorder-and-inorder-traversal/coloryourlife.py
create mode 100644 counting-bits/coloryourlife.py
create mode 100644 decode-ways/coloryourlife.py
create mode 100644 encode-and-decode-strings/coloryourlife.py
create mode 100644 valid-anagram/coloryourlife.py
diff --git a/construct-binary-tree-from-preorder-and-inorder-traversal/coloryourlife.py b/construct-binary-tree-from-preorder-and-inorder-traversal/coloryourlife.py
new file mode 100644
index 000000000..bc8e40952
--- /dev/null
+++ b/construct-binary-tree-from-preorder-and-inorder-traversal/coloryourlife.py
@@ -0,0 +1,23 @@
+# Definition for a binary tree node.
+# class TreeNode:
+# def __init__(self, val=0, left=None, right=None):
+# self.val = val
+# self.left = left
+# self.right = right
+class Solution:
+ # T: O(N)
+ # S: O(N)
+ def buildTree(self, preorder: List[int], inorder: List[int]) -> Optional[TreeNode]:
+ # preorder : root - left - right
+ # inorder : left - root - right
+ if not preorder and not inorder:
+ return None
+
+ root = TreeNode(preorder[0])
+ mid = inorder.index(preorder[0])
+
+ root.left = self.buildTree(preorder[1 : mid + 1], inorder[:mid])
+ root.right = self.buildTree(preorder[mid + 1 :], inorder[mid+1:])
+
+ return root
+
diff --git a/counting-bits/coloryourlife.py b/counting-bits/coloryourlife.py
new file mode 100644
index 000000000..6969b732c
--- /dev/null
+++ b/counting-bits/coloryourlife.py
@@ -0,0 +1,15 @@
+# T: O(N)
+# S: O(N)
+class Solution:
+ def countBits(self, n: int) -> List[int]:
+ res = []
+ for i in range(n + 1):
+ m = i
+ cnt = 0
+ while m > 0:
+ if m & 1 == 1:
+ cnt += 1
+ m = m >> 1
+ res.append(cnt)
+ return res
+
diff --git a/decode-ways/coloryourlife.py b/decode-ways/coloryourlife.py
new file mode 100644
index 000000000..b303fbfb5
--- /dev/null
+++ b/decode-ways/coloryourlife.py
@@ -0,0 +1,23 @@
+class Solution:
+ # T: O(N)
+ # S: O(N)
+ def numDecodings(self, s: str) -> int:
+ # The subproblem would be any portion of string
+ dp = {len(s): 1}
+
+ def dfs(i):
+ if i in dp:
+ return dp[i]
+ if s[i] == "0":
+ return 0
+
+ res = dfs(i + 1)
+ if i + 1 < len(s) and (
+ s[i] == "1" or s[i] == "2" and s[i + 1] in "0123456"
+ ):
+ res += dfs(i + 2)
+ dp[i] = res
+ return res
+
+ return dfs(0)
+
diff --git a/encode-and-decode-strings/coloryourlife.py b/encode-and-decode-strings/coloryourlife.py
new file mode 100644
index 000000000..3f454fc56
--- /dev/null
+++ b/encode-and-decode-strings/coloryourlife.py
@@ -0,0 +1,25 @@
+class Codec:
+ # T: O(n)
+ # S: O(1)
+ def encode(self, strs: List[str]) -> str:
+ """Encodes a list of strings to a single string.
+ """
+ res = ""
+ for s in strs:
+ res += str(len(s)) + "#" + s
+ return res
+
+
+ def decode(self, s: str) -> List[str]:
+ """Decodes a single string to a list of strings.
+ """
+ res, i = [], 0
+ while i < len(s):
+ j = i
+ while s[j] != "#":
+ j += 1
+ length = int(s[i:j])
+ res.append(s[j + 1 : j + 1 + length])
+ i = j + 1 + length
+ return res
+
diff --git a/valid-anagram/coloryourlife.py b/valid-anagram/coloryourlife.py
new file mode 100644
index 000000000..c6e4c6c4a
--- /dev/null
+++ b/valid-anagram/coloryourlife.py
@@ -0,0 +1,18 @@
+class Solution:
+ def isAnagram(self, s: str, t: str) -> bool:
+ # 1. sorting and compare : O(nlogn)
+ # 2. hashing: O(n)
+ # 3. array: O(n)
+ if len(s) != len(t):
+ return False
+ char_dict = defaultdict(int)
+ for c in s:
+ char_dict[c] += 1
+
+ for c in t:
+ char_dict[c] -= 1
+ if char_dict[c] < 0:
+ return False
+
+ return True
+