Valid Parentheses

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括号匹配，用栈即可

答案：

class Solution(object):
    def isValid(self, s):
        """
        :type s: str
        :rtype: bool
        """
        if s == '':
            return False
        stack = []
        for char in s:
            if char == '(' or char == '{' or char == '[':
                stack.append(char)
            else:
                if char == ')':
                    try:
                        if stack[-1] == '(':
                            stack.pop()
                        else:
                            return False
                    except:
                        return False
                elif char == ']':
                    try:
                        if stack[-1] == '[':
                            stack.pop()
                        else:
                            return False
                    except:
                            return False
                elif char == '}':
                    try:
                        if stack[-1] == '{':
                            stack.pop()
                        else:
                            return False
                    except:
                        return False
        if stack:
            return False
        return True