[Question 1] .Given an array `arr`, replace every element in that array with the greatest element among the elements to its right, and replace the last element with `-1`

```Example 1::
Input: arr = [17,18,5,4,6,1]
Output: [18,6,6,6,1,-1]
Explanation:
- index 0 --> the greatest element to the right of index 0 is index 1 (18).
- index 1 --> the greatest element to the right of index 1 is index 4 (6).
- index 2 --> the greatest element to the right of index 2 is index 4 (6).
- index 3 --> the greatest element to the right of index 3 is index 4 (6).
- index 4 --> the greatest element to the right of index 4 is index 5 (1).
- index 5 --> there are no elements to the right of index 5, so we put -1.```
``````// TC: O(N)
// SC: O(N)
func replaceElements(_ arr: [Int]) -> [Int] {
let arrayCount = arr.count
if arrayCount == 0 {return []}
let lastIndex = arrayCount - 1
var nums = Array.init(repeating: -1, count: arrayCount)
var curMax = arr[lastIndex]

nums[lastIndex] = -1// As per question requirement

for i in stride(from: lastIndex - 1, through: 0, by: -1) {
let temp = curMax
curMax = max(curMax, arr[i])
nums[i] = temp
}
return nums
}

var leaderArr1 = [10, 22, 12, 3, 0, 6]

[Question 2] : Problem Statement: Given an array, print all the elements which are leaders. A Leader is an element that is greater than all of the elements on its right side in the array

```Example 1:
Input:
arr = [4, 7, 1, 0]
Output:
7 1 0
Explanation:
Rightmost element is always a leader. 7 and 1 are greater than the elements in their right side.```
``````// TC O(N)
// SC O(N)
var leader = arr.last ?? 0