Replace every element with the greatest element on right side

Given an array of integers, replace every element with the next greatest element (greatest element on the right side) in the array. Since there is no element next to the last element, replace it with -1. For example, if the array is {16, 17, 4, 3, 5, 2}, then it should be modified to {17, 5, 5, 5, 2, -1}.

The question is very similar to this post and solutions are also similar.

A naive method is to run two loops. The outer loop will one by one pick array elements from left to right. The inner loop will find the greatest element present after the picked element. Finally the outer loop will replace the picked element with the greatest element found by inner loop. The time complexity of this method will be O(n*n).
A tricky method is to replace all elements using one traversal of the array. The idea is to start from the rightmost element, move to the left side one by one, and keep track of the maximum element. Replace every element with the maximum element.

#include <stdio.h>   /* Function to replace every element with the    next greatest element */ void nextGreatest(int arr[], int size) {   // Initialize the next greatest element   int max_from_right =  arr[size-1];     // The next greatest element for the rightmost element   // is always -1   arr[size-1] = -1;     // Replace all other elements with the next greatest   for(int i = size-2; i >= 0; i--)   {     // Store the current element (needed later for updating     // the next greatest element)     int temp = arr[i];       // Replace current element with the next greatest     arr[i] = max_from_right;       // Update the greatest element, if needed     if(max_from_right < temp)        max_from_right = temp;   } }   /* A utility Function that prints an array */ void printArray(int arr[], int size) {   int i;   for (i=0; i < size; i++)     printf("%d ", arr[i]);   printf("\n"); }   /* Driver program to test above function */ int main() {   int arr[] = {16, 17, 4, 3, 5, 2};   int size = sizeof(arr)/sizeof(arr[0]);   nextGreatest (arr, size);   printf ("The modified array is: \n");   printArray (arr, size);   return (0); }

Output:

The modified array is:
17 5 5 5 2 -1

Time Complexity: O(n) where n is the number of elements in array.

Please write comments if you find any of the above codes/algorithms incorrect, or find other ways to solve the same problem.