cassidoo-interview-question-august-14

validParantheses.java

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