Leetcode-921 Minimum Add to Make Parentheses Valid(使括号有效的最少添加)

class Solution
{
    public:
        int minAddToMakeValid(string S)
        {
            stack<char> s;
            int result = 0;
            for(auto c:S)
            {
                if(c=='(')
                    s.push('(');
                else
                {
                    if(s.empty())
                        result ++;
                    else
                    {
                        s.pop();
                    }
                }
            }
            while(!s.empty())
            {
                s.pop();
                result ++;
            }
            return result;
        }
};