Problem

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.

After doing so, return the array.

Examples

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.

Example 2:

Input:
arr = [400]
Output:
 [-1]

Solution

Method 1 - Starting From End of Array

Code:

public int[] replaceElements(int[] arr) {
	int n = arr.length;
	int max = -1; // max from right
	for (int i = n - 1; i >= 0; i--) {
		int temp = arr[i];
		arr[i] = max;
		max = Math.max(max, temp);
	}
	return arr;
}