Leetcode 921

Author: Kondareddy1209

Leetcode/Leetcode_921.py

@@ -0,0 +1,56 @@
+class Solution:
+    def minAddToMakeValid(self, s: str) -> int:
+        """
+        LeetCode 921 - Minimum Add to Make Parentheses Valid
+
+        Approach:
+        - Use a stack to keep track of unmatched opening parentheses '('.
+        - Traverse each character in the string:
+            1. If the character is '(', push it onto the stack.
+            2. If the character is ')':
+                - If the stack is not empty, pop one '(' as it forms a valid pair.
+                - Otherwise, increment 'count' because an extra '(' is needed.
+        - After the traversal, any remaining '(' in the stack require matching ')'.
+
+        Return:
+        - count + len(stack)
+          where:
+            count      -> number of unmatched ')'
+            len(stack) -> number of unmatched '('
+
+        Example:
+        Input: s = "()))(("
+
+        Traversal:
+        '(' -> push
+        ')' -> pop
+        ')' -> stack empty -> count = 1
+        ')' -> stack empty -> count = 2
+        '(' -> push
+        '(' -> push
+
+        Result:
+        count = 2
+        len(stack) = 2
+        Answer = 2 + 2 = 4
+
+        Time Complexity: O(n)
+            - Each character is processed once.
+
+        Space Complexity: O(n)
+            - In the worst case, the stack stores all opening parentheses.
+        """
+
+        count = 0
+        stack = []
+
+        for i in range(len(s)):
+            if s[i] == "(":
+                stack.append(s[i])
+            else:
+                if stack:
+                    stack.pop()
+                else:
+                    count += 1
+
+        return count + len(stack)