Leetcode(20) Valid Parentheses

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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.

解法：

利用栈做匹配，正括号都入栈，反括号入栈时查看有无匹配，有则对应正括号出栈，否则匹配失败，字符串不合法。当最终栈空时匹配成功，否则失败。特别注意“( [ ) ]”的情况，是不合法的。代码如下：

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class Solution:
    def isValid(self, s):
        """
        :type s: str
        :rtype: bool
        """
        l = [];
        for c in s:
            if(c == '(' or c == '[' or c == '{'):
                l.append(c);
            elif(c == ')'):
                if(len(l) != 0 and l[-1] == '('):
                    l = l[:-1];
                else:
                    return False;
            elif(c == ']'):
                if(len(l) != 0 and l[-1] == '['):
                    l = l[:-1];
                else:
                    return False;
            elif(c == '}'):
                if(len(l) != 0 and l[-1] == '{'):
                    l = l[:-1];
                else:
                    return False;
        if(len(l) == 0):
            return True;
        return False;