503. Next Greater Element II

/*
Time Complexity: O(n)
Space Complexity: O(n)

n = length of nums array.
*/
class Solution {
    public int[] nextGreaterElements(int[] nums) throws IllegalArgumentException {
        if (nums == null) {
            throw new IllegalArgumentException("Input nums array is null");
        }

        if (nums.length == 0) {
            return new int[0];
        }

        int len = nums.length;
        int[] result = new int[len];
        Arrays.fill(result, -1);
        Stack<Integer> stack = new Stack();

        for (int i = 0; i < len * 2; i++) {
            int num = nums[i % len];
            while (!stack.isEmpty() && nums[stack.peek()] < num) {
                result[stack.pop()] = num;
            }
            if (i < len) {
                stack.push(i);
            }
        }

        return result;
    }
}


/*
Time Complexity: O(n)
Space Complexity: O(n)

n = length of nums array.
*/
class Solution {
    public int[] nextGreaterElements(int[] nums) throws IllegalArgumentException {
        if (nums == null) {
            throw new IllegalArgumentException("Input nums array is null");
        }

        if (nums.length == 0) {
            return new int[0];
        }

        int len = nums.length;
        int[] result = new int[len];
        Stack<Integer> stack = new Stack();

        for (int i = len*2 -1; i >= 0; i--) {
            while (!stack.isEmpty() && nums[stack.peek()] <= nums[i % len]) {
                stack.pop();
            }
            if (i < len) {
                result[i] = stack.isEmpty() ? -1 : nums[stack.peek()];
            }
            stack.push(i % len);
        }

        return result;
    }
}