Replace every element of the array by its previous element

Given an array arr, the task is to replace each element of the array with the element that appears before it and replace the first element with -1. 

Examples:

Input: arr[] = {5, 1, 3, 2, 4} 
Output: -1 5 1 3 2

Input: arr[] = {6, 8, 32, 12, 14, 10, 25 } 
Output: -1 6 8 32 12 14 10 

Approach: Traverse the array from n – 1 to 1 and update arr[i] = arr[i-1]. In the end set a[0] = -1 and print the contents of the updated array.

Below is the implementation of the above approach: 

C++

// C++ program to replace every element of the array
// with the element that appears before it
#include <bits/stdc++.h>
using namespace std;

// Function to print the array after replacing every element
// of the array with the element that appears before it
void updateArray(int arr[], int n)
{
    // Update array
    for (int i = n - 1; i > 0; i--)
        arr[i] = arr[i - 1];

    // Change the first element to -1
    arr[0] = -1;

    // Print the updated array
    for (int i = 0; i < n; i++)
        cout << arr[i] << " ";
}

// Driver program
int main()
{
    int arr[] = { 5, 1, 3, 2, 4 };
    int N = sizeof(arr) / sizeof(arr[0]);
    updateArray(arr, N);
    return 0;
}

C

// C program to replace every element of the array
// with the element that appears before it
#include <stdio.h>

// Function to print the array after replacing every element
// of the array with the element that appears before it
void updateArray(int arr[], int n)
{
    // Update array
    for (int i = n - 1; i > 0; i--)
        arr[i] = arr[i - 1];

    // Change the first element to -1
    arr[0] = -1;

    // Print the updated array
    for (int i = 0; i < n; i++)
      printf("%d ",arr[i]);
}

// Driver program
int main()
{
    int arr[] = { 5, 1, 3, 2, 4 };
    int N = sizeof(arr) / sizeof(arr[0]);
    updateArray(arr, N);
    return 0;
}

// This code is contributed by kothavvsaakash.

Java

// Java program to replace every element
// of the array with the element that
// appears before it
class GFG
{

// Function to print the array after
// replacing every element of the
// array with the element that appears
// before it
static void updateArray(int arr[], int n)
{
    // Update array
    for (int i = n - 1; i > 0; i--)
        arr[i] = arr[i - 1];

    // Change the first element to -1
    arr[0] = -1;

    // Print the updated array
    for (int i = 0; i < n; i++)
        System.out.print(arr[i] + " ");
}

// Driver Code
public static void main(String []args)
{
    int arr[] = { 5, 1, 3, 2, 4 } ;
    int N = arr.length ;
    updateArray(arr, N);
}
}

// This code is contributed by Ryuga

Python3

# Python 3 program to replace every element
# of the array with the element that appears
# before it

# Function to print the array after replacing
# every element of the array with the element
# that appears before it
def updateArray(arr, n):

    # Update array
    i = n - 1
    while(i > 0):
        arr[i] = arr[i - 1]
        i -= 1

    # Change the first element to -1
    arr[0] = -1

    # Print the updated array
    for i in range(0, n, 1):
        print(arr[i], end = " ")

# Driver Code
if __name__ == '__main__':
    arr = [5, 1, 3, 2, 4]
    N = len(arr)
    updateArray(arr, N)

# This code is contributed by
# Surendra_Gangwar

C#

// C# program to replace every element
// of the array with the element that
// appears before it
using System;

class GFG
{

// Function to print the array after
// replacing every element of the
// array with the element that appears
// before it
static void updateArray(int[] arr, int n)
{
    // Update array
    for (int i = n - 1; i > 0; i--)
        arr[i] = arr[i - 1];

    // Change the first element to -1
    arr[0] = -1;

    // Print the updated array
    for (int i = 0; i < n; i++)
        Console.Write(arr[i] + " ");
}

// Driver Code
public static void Main()
{
    int[] arr = { 5, 1, 3, 2, 4 } ;
    int N = arr.Length ;
    updateArray(arr, N);
}
}

// This code is contributed
// by Akanksha Rai

PHP

<?php
// PHP program to replace every element
// of the array with the element that
// appears before it

// Function to print the array after
// replacing every element of the array
// with the element that appears before it
function updateArray($arr, $n)
{
    // Update array
    for ($i = $n - 1; $i > 0; $i--)
        $arr[$i] = $arr[$i - 1];

    // Change the first element to -1
    $arr[0] = -1;

    // Print the updated array
    for ($i = 0; $i < $n; $i++)
        echo $arr[$i] ," ";
}

// Driver Code
$arr = array(5, 1, 3, 2, 4 );
$N = sizeof($arr);
updateArray($arr, $N);

// This code is contributed
// by Sach_Code
?>

Javascript

<script>
// Java script program to replace every element
// of the array with the element that
// appears before it

// Function to print the array after
// replacing every element of the
// array with the element that appears
// before it
function updateArray(arr,n)
{
    // Update array
    for (let i = n - 1; i > 0; i--)
        arr[i] = arr[i - 1];

    // Change the first element to -1
    arr[0] = -1;

    // Print the updated array
    for (let i = 0; i < n; i++)
        document.write(arr[i] + " ");
}

// Driver Code

    let arr =[ 5, 1, 3, 2, 4 ];
    let N = arr.length ;
    updateArray(arr, N);

// This code is contributed by sravan kumar G
</script>

Output

-1 5 1 3 2 

Complexity Analysis:

• Time Complexity: O(n)
• Auxiliary Space: O(1)