学步园

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.

这个就是栈的基本应用了，如果是左括号，就入栈，右括号，就将栈顶元素弹出并与右括号匹配是否成功，成功就继续之前的操作，失败返回false，当遍历完后需要判断栈是否为空，不为空说明有位匹配的左括号，返回false

bool isValid(string s) {
        stack<char> sta;
        char c;
        for(int i = 0; i < s.size(); i++){
            if(s[i] == '(' || s[i] == '[' || s[i] == '{'){
                sta.push(s[i]);
                continue;
            }
            if(sta.empty())
                return false;
            c = sta.top();
            if((c == '(' && s[i] == ')') || (c == '[' && s[i] == ']') || (c == '{' && s[i] == '}')){
                sta.pop();
                continue;
            }else
                return false;
        }
        if(sta.empty())
            return true;
        else
            return false;
    }