LeetCode 496

class Solution {
    public int[] nextGreaterElement(int[] nums1, int[] nums2) {
        int n = nums2.length;
        int[] highRight = new int[n];
        Deque<Integer> stk = new LinkedList<>();
        Map<Integer, Integer> map = new HashMap<>();
        for (int i = n - 1; i >= 0; i--) {
            while (!stk.isEmpty() && nums2[i] >= nums2[stk.peek()]) stk.pop();
            highRight[i] = stk.isEmpty() ? n : stk.peek();
            stk.push(i);
            map.put(nums2[i], i);
        }
        int m = nums1.length;
        int[] res = new int[m];
        Arrays.fill(res, -1);
        for (int i = 0; i < m; i++) {
            if (map.containsKey(nums1[i])) {
                int t = map.get(nums1[i]);
                if (highRight[t] != n) res[i] = nums2[highRight[t]];
            }
        }
        return res;
    }
}