有效的括号序列——算法面试刷题4（for google），考察stack

class Solution:
    """
    @param s: A string
    @return: whether the string is a valid parentheses
    """
    def isValidParentheses(self, s):
        # write your code here
        match_par = {"(": ")", "[": "]", "{": "}"}
        l_par = set(match_par.keys())
        r_par = set(match_par.values())
        stack = []
        for c in s:
            if c in l_par:
                stack.append(c)
            elif c in r_par:
                if not stack or match_par[stack.pop()] != c:
                    return False
            else:
                pass
        return len(stack) == 0

class Solution(object):
    ‘‘‘
    题意：输入一个只包含括号的字符串，判断括号是否匹配
    模拟堆栈，读到左括号压栈，读到右括号判断栈顶括号是否匹配
    ‘‘‘
    def isValidParentheses(self, s):
        stack = []
        for ch in s:
            # 压栈
            if ch == ‘{‘ or ch == ‘[‘ or ch == ‘(‘:
                stack.append(ch)
            else:
                # 栈需非空
                if not stack:
                    return False
                # 判断栈顶是否匹配
                if ch == ‘]‘ and stack[-1] != ‘[‘ or ch == ‘)‘ and stack[-1] != ‘(‘ or ch == ‘}‘ and stack[-1] != ‘{‘:
                    return False
                # 弹栈
                stack.pop()
        return not stack