valid parenthesis string.cpp

class Solution {
public:
    bool checkValidString(string s) {
        int l=0,h=0;
        for(char it : s){
            l+= it=='(' ? 1: -1;
            h+= it!= ')' ? 1: -1;
            if(h<0) break;
            l=max(l,0);
        }
        return l==0;
    }
};