20. Valid Parentheses

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.

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括号匹配

C++（3ms）：

class Solution {
public:
    bool isValid(string s) {
        stack<char> m ;
        for (char c : s){
            if (c == '(' || c=='{' || c=='['){
                   m.push(c) ;
            }else{
                if (m.empty())
                    return false ;
                if (c == ')' && m.top()!='(')
                    return false ;
                if (c == '}' && m.top()!='{')
                    return false ;
                if (c == ']' && m.top()!='[')
                    return false ;
                m.pop();
            }
        }
        if (m.empty())
           return true ;
        else
           return false ;
    }
};