Replace Elements with Greatest Element on Right Side - Array - Easy - LeetCode

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.

Example 1:

Input: arr = [17,18,5,4,6,1]

Output: [18,6,6,6,1,-1]

Constraints:

1 <= arr.length <= 10^4

1 <= arr[i] <= 10^5

Solution:

using System;
using System.Collections.Generic;
using System.Text;

namespace LeetCode.AskGif.Easy.Array
{
 public class ReplaceElementsSoln
 {
 public int[] ReplaceElements(int[] arr)
 {
 var temp = new int[arr.Length];
 temp[arr.Length - 1] = arr[arr.Length - 1];
 for (int i = arr.Length-2; i >= 0; i--)
 {
 if (arr[i] > temp[i + 1])
 {
 temp[i] = arr[i];
 }
 else
 {
 temp[i] = temp[i + 1];
 }
 }

 var res = new int[arr.Length];
 for (int i = 0; i < arr.Length-1; i++)
 {
 res[i] = temp[i + 1];
 }
 res[arr.Length - 1] = -1;

 return res;
 }
 }
}

Time Complexity: O(n)

Space Complexity: O(n)

Unit Tests:

using LeetCode.AskGif.Easy.Array;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using System;
using System.Collections.Generic;
using System.Text;

namespace CodingUnitTest.Easy.Array
{
 [TestClass]
 public class ReplaceElementsSolnTests
 {
 [TestMethod]
 public void ReplaceElementsSoln_First()
 {
 var arr = new int[] { 17, 18, 5, 4, 6, 1 };
 var output = new int[] { 18, 6, 6, 6, 1, -1 };
 var res = new ReplaceElementsSoln().ReplaceElements(arr);

 AreEqual(res, output);
 }

 private void AreEqual(int[] res, int[] output)
 {
 Assert.AreEqual(res.Length, output.Length);
 for (int i = 0; i < res.Length; i++)
 {
 Assert.AreEqual(res[i], output[i]);
 }
 }
 }
}