Merge pull request #2459 from yerim01/main

[yerim01] WEEK 03 solutions

Author: yerim01

number-of-1-bits/yerim01.py

@@ -0,0 +1,19 @@
+# Goal: Given a positive int n, return the number of set bits in binary.
+# Approach:
+# Divide by 2 and check the remainder to determine the last bit.
+# If the remainder is 1, update the variable 'count'.
+# Repeat until n becomes 0.
+# Time Complexity: O(logn)
+# - We process each bit of n.
+# Space Complexity: O(1)
+# - We use only one variable 'count'.
+class Solution:
+    def hammingWeight(self, n: int) -> int:
+        count = 0
+
+        while n != 0:
+            if n % 2 == 1:
+                count += 1
+            n = n // 2
+        
+        return count

valid-palindrome/yerim01.py

@@ -0,0 +1,31 @@
+# Goal: Return true if it's a palindrome. If it's not, return false
+# - palindrome: a string that reads the same forward and backward
+# Time Complexity: O(n)
+# - Building string is O(n) + Two pointer check is O(n).
+# Space Complexity: O(n)
+# - We use a new string of size s.
+class Solution:
+    def isPalindrome(self, s: str) -> bool:
+        chars = []
+
+        # Trim 's' to contain only alphanumerical characters
+        for ch in s:
+            if ch.isalnum():
+                chars.append(ch.lower()) # make it case-insensitive
+
+        new_s = "".join(chars)
+
+        # Use two pointers
+        # ptr1 -> starting index ptr2 -> ending index
+        ptr1 = 0
+        ptr2 = len(new_s) - 1
+
+        while ptr1 < ptr2: # O(n) time
+            # Return false if ptr1 and ptr2 point to different char
+            if new_s[ptr1] != new_s[ptr2]:
+                return False
+            ptr1 += 1
+            ptr2 -= 1
+
+        # Otherwise, return true
+        return True