Valid Parenthesis

//  https://leetcode.com/explore/challenge/card/january-leetcoding-challenge-2021/581/week-3-january-15th-january-21st/3610/
class Solution {
public:
    bool isValid(string s) {
        std::stack<char> st;
        for(auto ch : s) {
            if(ch == '(' || ch == '{' || ch == '[') {
                st.push(ch);
            } else if(ch == ')') {
                if(st.size() <= 0 || st.top() != '(')
                    return false;
                st.pop();
            } else if(ch == '}') {
                if(st.size() <= 0 || st.top() != '{')
                    return false;
                st.pop();
            } else if(ch == ']') {
                if(st.size() <= 0 || st.top() != '[')
                    return false;
                st.pop();
            }
        }
        return st.empty();
    }
};