LeetCode 581

class Solution {
    public int findUnsortedSubarray(int[] nums) {
        Deque<Integer> stk = new LinkedList<>();
        int n = nums.length;
        int left = n;
        for (int i = 0; i < n; i++) {
            while (!stk.isEmpty() && nums[i] < nums[stk.peek()]) 
                left = Math.min(left, stk.pop());
            stk.push(i);
        }
        if (left == n) return 0;
        stk.clear();
        int right = -1;
        for (int i = n - 1; i >= 0; i--) {
            while (!stk.isEmpty() && nums[i] > nums[stk.peek()])
                right = Math.max(right, stk.pop());
            stk.push(i);
        }
        if (right == -1) return 0;
        return right - left + 1;
    }
}