Description
Given a string containing just the characters '('
, ')'
, '{'
, '}'
, '['
and ']'
, determine if the input string is valid.
An input string is valid if:
- Open brackets must be closed by the same type of brackets.
- 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
Answer - 用到Stack
class Solution: def isValid(self, s): """ :type s: str :rtype: bool """ pairs = {']':'[', ')':'(', '}':'{'} stack = [s[0]] for i in range(1,len(s)): stack.append(s[i]) if stack[-1] in pairs and stack[-2] == pairs[stack[-1]]: stack.pop() stack.pop() if len(stack)>=1: return False return True