leetcode020-python 有效括号

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:

解题要点：

1.栈的功能和配对，栈可以用列表去实现，一一配对的功能用两个字符串的下表去对应（当然也可以有其他方法，比如写一个判断的函数之类的）；

class Solution:
    def isValid(self, s):
        """
        :type s: str
        :rtype: bool
        """
        lt = []
        left = "{[("
        right = "}])"
        for i in s:
            if i in left:
                lt.append(i)
            else:
                if len(lt) != 0:
                    c = lt.pop()
                    if left.index(c) != right.index(i):
                        return False
                else:
                    return False
        if len(lt) != 0:
            return False
        else:
            return True