Next Greater Element in Swift

The next greater element of some element x in an array is the first greater element that is to the right of x in the same array.

Given an array of integers nums, return an array containing the indices of the next greater element for each number in nums.

If a number doesn't have a next greater element, denote that with -1.

Example 1:

Input: nums = [1, 3, 2, 4]
Output: [1, 3, 3, -1]
Explanation: The next greater element for each value of nums is as follows:
- next greater element for 1 is 3 which is located at index 1
- next greater element for 3 is 4 which is located at index 3
- next greater element for 2 is 4 which is located at index 3
- 4 is the last and doesn't have a next greater element so we mark it with -1

Example 2:

Input: nums = [7, 3, 2, 6, 11, 9, 8, 10, 13]
Output: [4, 3, 3, 4, 8, 7, 7, 8, -1]