[leetCode] 20. Valid Parentheses (Python)

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

 

An input string is valid if:

1. Open brackets must be closed by the same type of brackets.
2. Open brackets must be closed in the correct order.

Note that an empty string is also considered valid.

 

Example 1:

Input: "()"
Output: true

Example 2:

Input: "()[]{}"
Output: true

Example 3:

Input: "(]"
Output: false

Example 4:

Input: "([)]"
Output: false

Example 5:

Input: "{[]}"
Output: true

Solution

class Solution:
    def isValid(self, s: str) -> bool:
        s_list = list(s)
        
        answer = True
        
        stack = []
        
        for s in s_list:
            if s == '[' or s == '(' or s == '{':
                stack.append(s)
            elif len(stack) != 0:
                if (s == ']' and stack[-1] == '[') or (s == '}' and stack[-1] == '{') or (s == ')' and stack[-1] == '('): 
                    stack.pop()
                else:
                    answer = False
                    break
            else:
                answer = False
                break
                
        if len(stack) != 0:
            answer = False
            
        return answer

 

SOMJANG/CODINGTEST_PRACTICE