Max Valid Parentheses

MaxValidParentheses.java

public class Solution {
    public int longestValidParentheses(String s) {
        Stack<Integer> stk = new Stack<Integer>();
        int left = -1;
        int maxCount = 0;
        for (int i = 0; i < s.length(); i++){
            if (s.charAt(i) == '('){
                stk.push(i);
            }
            else{
                if (stk.empty()){
                    left = i;
                }
                else{
                    stk.pop();
                    if (stk.empty()){
                         maxCount = Math.max(maxCount, i-left);
                    }
                    else{
                        maxCount = Math.max(maxCount, i - stk.peek());
                    }
                }
            }
        }
        return maxCount;
    }
}