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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}. 

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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).




// THIS CODE IS CONTRIBUTED BY KIRTI AGARWAL(KIRTIAGARWAL23121999)
// C++ Program to replace every element with the greatest
// element on right side
#include <bits/stdc++.h>
using namespace std;
   
// Function to replace every element with the
// next greatest element
void nextGreatest(int arr[], int n){
    for(int i = 0; i<n; i++){
        int max_value = -1;
        for(int j = i+1; j<n; j++){
            max_value = max(max_value, arr[j]);
        }
        arr[i] = max_value;
    }
}
   
// A utility Function that prints an array 
void printArray(int arr[], int size){
    for (int i = 0; i < size; i++)
        cout << arr[i] << " ";
    cout << endl;
}
   
// 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);
    cout << "The modified array is: \n";
    printArray (arr, size);
    return (0);
}




// Java Program to replace every element with the greatest
// element on right side
class Main {
    // Function to replace every element with the
    // next greatest element
    static void nextGreatest(int arr[], int n)
    {
        for (int i = 0; i < n; i++) {
            int max_value = -1;
            for (int j = i + 1; j < n; j++) {
                max_value = Math.max(max_value, arr[j]);
            }
            arr[i] = max_value;
        }
    }
  
    // A utility Function that prints an array
    static void printArray(int arr[], int size)
    {
        for (int i = 0; i < size; i++)
            System.out.print(arr[i] + " ");
        System.out.println();
    }
  
    // Driver program to test above function
    public static void main(String[] args)
    {
        int arr[] = { 16, 17, 4, 3, 5, 2 };
        int size = arr.length;
        nextGreatest(arr, size);
        System.out.println("The modified array is: ");
        printArray(arr, size);
    }
}




# Function to replace every element with the next greatest element
def nextGreatest(arr, n):
    for i in range(n):
        max_value = -1
        for j in range(i+1, n):
            max_value = max(max_value, arr[j])
        arr[i] = max_value
  
# A utility Function that prints an array
  
  
def printArray(arr, size):
    for i in range(size):
        print(arr[i], end=" ")
    print()
  
  
# Driver program to test above function
if __name__ == '__main__':
    arr = [16, 17, 4, 3, 5, 2]
    size = len(arr)
    nextGreatest(arr, size)
    print("The modified array is:")
    printArray(arr, size)




using System;
  
public class MainClass
{
    // Function to replace every element with the
    // next greatest element
    static void NextGreatest(int[] arr, int n)
    {
        for (int i = 0; i < n; i++)
        {
            int max_value = -1;
            for (int j = i + 1; j < n; j++)
            {
                max_value = Math.Max(max_value, arr[j]);
            }
            arr[i] = max_value;
        }
    }
  
    // A utility Function that prints an array
    static void PrintArray(int[] arr, int size)
    {
        for (int i = 0; i < size; i++)
        {
            Console.Write(arr[i] + " ");
        }
        Console.WriteLine();
    }
  
    // Driver program to test above function
    public static void Main(string[] args)
    {
        int[] arr = { 16, 17, 4, 3, 5, 2 };
        int size = arr.Length;
        NextGreatest(arr, size);
        Console.WriteLine("The modified array is: ");
        PrintArray(arr, size);
    }
}




// JavaScript Program to replace every element with 
// the greatest element on right side
  
// Function to replace every element with the next greatest element
function nextGreatest(arr, n) {
  for(let i = 0; i < n; i++) {
    let max_value = -1;
    for(let j = i + 1; j < n; j++) {
      max_value = Math.max(max_value, arr[j]);
    }
    arr[i] = max_value;
  }
}
  
// A utility function that prints an array
function printArray(arr, size) {
  for(let i = 0; i < size; i++) {
    console.log(arr[i] + " ");
  }
  console.log("\n");
}
  
// Driver program to test above function
let arr = [16, 17, 4, 3, 5, 2];
let size = arr.length;
nextGreatest(arr, size);
console.log("The modified array is: ");
printArray(arr, size);

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

Time Complexity: O(N^2)

Auxiliary Space: O(1)

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. 




// C++ Program to replace every element with the greatest 
// element on right side 
#include <bits/stdc++.h>
using namespace std;
  
/* Function to replace every element with the 
next greatest element */
void nextGreatest(int arr[], int size) 
    //Initialise maxFromRight with -1
    int maxFromRight = -1;
    int n = size;
      // run loop from last and replace maxFromRight with the element in the array
    for(int i= n-1; i>=0;i--) {
      int temp = maxFromRight;
      if(arr[i]> maxFromRight){
        //replacing only array element with maxFromRight in case element is bigger
        maxFromRight = arr[i];
      }
      arr[i] = temp;
    }
    return;
  
/* A utility Function that prints an array */
void printArray(int arr[], int size) 
    int i; 
    for (i = 0; i < size; i++) 
        cout << arr[i] << " "
    cout << endl; 
  
/* 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); 
    cout << "The modified array is: \n"
    printArray (arr, size); 
    return (0); 
  
// This is code is contributed by rathbhupendra




// C Program to replace every element with the greatest
// element on right side
#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);
}




// Java Program to replace every element with the 
// greatest element on right side
import java.io.*;
  
class NextGreatest 
{
    /* Function to replace every element with the
       next greatest element */
    static void nextGreatest(int arr[])
    {
        int size = arr.length;
  
        // 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 */
    static void printArray(int arr[])
    {
        for (int i=0; i < arr.length; i++)
        System.out.print(arr[i]+" ");
    }
  
    public static void main (String[] args)
    {
        int arr[] = {16, 17, 4, 3, 5, 2};
        nextGreatest (arr);
        System.out.println("The modified array:");
        printArray (arr);
    }
}
/*This code is contributed by Devesh Agrawal*/




# Python Program to replace every element with the 
# greatest element on right side
  
# Function to replace every element with the next greatest
# element
def nextGreatest(arr):
  
    size = len(arr)
  
    # Initialize the next greatest element
    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 i in range(size-2,-1,-1):
  
        # Store the current element (needed later for updating
        # the next greatest element)
        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
  
# Utility function to print an array
def printArray(arr):
    for i in range(0,len(arr)):
        print (arr[i],end=" ")
  
# Driver function to test above function
arr = [16, 17, 4, 3, 5, 2]
nextGreatest(arr)
print ("Modified array is")
printArray(arr)
# This code is contributed by Devesh Agrawal




// C# Program to replace every element with the 
// greatest element on right side
using System;
  
class GFG {
      
    /* Function to replace every element with 
    the    next greatest element */
    static void nextGreatest(int []arr)
    {
        int size = arr.Length;
  
        // 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 */
    static void printArray(int []arr)
    {
        for (int i=0; i < arr.Length; i++)
        Console.Write(arr[i]+" ");
    }
  
    public static void Main ()
    {
        int []arr = {16, 17, 4, 3, 5, 2};
        nextGreatest (arr);
        Console.WriteLine("The modified array:");
        printArray (arr);
    }
}
  
/* This code is contributed by vt_m.*/




<?php
// PHP Program to replace every element with 
// the greatest element on right side 
  
/* Function to replace every element 
with the next greatest element */
function nextGreatest(&$arr, $size
    // Initialize the next greatest element 
    $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($i = $size - 2; $i >= 0; $i--) 
    
        // Store the current element (needed 
        // later for updating the next 
        // greatest element) 
        $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
function printArray($arr, $size
    for ($i = 0; $i < $size; $i++) 
        echo $arr[$i] . " "
    echo "\n"
  
// Driver Code
$arr = array(16, 17, 4, 3, 5, 2); 
$size = count($arr); 
nextGreatest ($arr, $size); 
echo "The modified array is: \n"
printArray ($arr, $size); 
  
// This code is contributed by 
// rathbhupendra
?>




<script>
  
// JavaScript Program to replace every element with the greatest 
// element on right side 
  
/* Function to replace every element with the 
next greatest element */
   function nextGreatest(arr,size) 
        
    // Initialize the next greatest element 
       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(let  i = size-2; i >= 0; i--) 
    
        // Store the current element (needed later for updating 
        // the next greatest element) 
         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 */
      function  printArray(arr,size) 
     var i; 
    for ( let i = 0; i < size; i++) 
      document.write(arr[i]  + " " ); 
    
/* Driver program to test above function */
  
     arr = new Array (16, 17, 4, 3, 5, 2); 
      size = arr.length; 
    nextGreatest (arr, size); 
      document.write ("The modified array is: " + "<br>"+ " \n"); 
        
    printArray (arr, size); 
      
    // This code is contributed by simranarora5sos
      
 </script>

Output: 

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

Time Complexity: O(n) where n is the number of elements in array.
Auxiliary Space: O(1)
 

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


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