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.

题目大意：

class Solution {
public:
    bool isValid(std::string s) {
        const int size = s.size();
        std::stack<char> v;
        
        if (size % 2) {
            return false;
        } else if (size == 0) {
            return true;
        }
        
        for (int i = 0; i < size; ++i) {
            const char tmp = s[i];
            if (tmp == '(' || tmp == '{' || tmp == '[') {
                v.push(tmp);
            } else if ((!v.empty()) && ((tmp == ')' && v.top() == '(') || (tmp == ']' && v.top() == '[') || (tmp == '}' && v.top() == '{'))) {
                v.pop();
            } else {
                return false;
            }
        }
        return v.empty();
    }
};

bool isValid(string s) {
        
        stack<char> pare;
        
        for(auto c:s){
            if(c=='(' || c=='{' || c=='['){
                pare.push(c);
            }else{
                if(pare.empty()) return false;
                
                if(c-pare.top()>2) return false;
                //becasue in Ascii, (:40, ):41, [:91, ]:93, {:123, }:125
                pare.pop();
            }
        }
        return pare.empty();
}