Add solution of valid parenthese

Author: sbk1014

valid-parentheses/bhyun-kim.py

@@ -0,0 +1,43 @@
+"""
+20. Valid Parentheses
+https://leetcode.com/problems/valid-parentheses/description/
+
+Solution
+    Uses a stack to check if the parentheses are valid.
+
+    1. Initialize an empty stack.
+    2. Iterate through each character in the string.
+    3. If the character is an opening parenthesis, 
+        push it to the stack.
+    4. If the character is a closing parenthesis,
+        pop the stack and check if the opening parenthesis matches.
+    5. If the stack is empty, return True.
+    6. Otherwise, return False.
+
+Time complexity: O(n)
+Space complexity: O(n)
+"""
+
+
+class Solution:
+    def isValid(self, s: str) -> bool:
+        stack = ""
+        opening = ["(", "[", "{"]
+        closing = [")", "]", "}"]
+
+        for _s in s:
+            if _s in opening:
+                stack = _s + stack
+            else:
+                if stack:
+                    if opening[closing.index(_s)] == stack[0]:
+                        stack = stack[1:]
+                    else:
+                        return False
+                else:
+                    return False
+
+        if len(stack) > 0:
+            return False
+        else:
+            return True