[勇者闖LeetCode] 20. Valid Parentheses

[勇者闖LeetCode] 20. Valid Parentheses

Description

Given a string containing just the characters ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[’ and ‘]’, determine if the input string is valid.
The brackets must close in the correct order, “()” and “()[]{}” are all valid but “(]” and “([)]” are not.

Information

• Tags: Stack | String
• Difficulty: Easy

Solution

用棧存儲需要遇到的右括號。掃描字符串時遇到左括號則其對應的右括號入棧，遇到右括號則出棧並判斷兩個右括號是否相同，若不相同則返回false。掃描結束後，若棧內還有元素，則返回false。

class Solution(object):
    def isValid(self, s):
        """
        :type s: str
        :rtype: bool
        """
        l = {"(": ")", "[": "]", "{": "}"}
        ans = []
        for x in s:
            if x in l:
                ans.append(l[x])
            elif (len(ans) == 0 or ans.pop() != x):
                return False
        return False if len(ans) > 0 else True