# 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

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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 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; }

## 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

 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 ?>

Output:

-1 5 1 3 2

Time Complexity : O(n)

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