[勇者闯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.
Tags: Stack | StringDifficulty: Easy
Solution
用栈存储需要遇到的右括号。扫描字符串时遇到左括号则其对应的右括号入栈，遇到右括号则出栈并判断两个右括号是否相同，若不相同则返回false。扫描结束后，若栈内还有元素，则返回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
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