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Replace every element with the greatest element on its left side
• Difficulty Level : Basic
• Last Updated : 29 Apr, 2021

Given an array of integers, the task is to replace every element with the greatest element on its left side.
Note: Replace the first element with -1 as it has no element in its left.
Examples:

```Input: arr[] = {4, 5, 2, 1, 7, 6}
Output: -1 4 5 5 5 7
Since, 4 has no element in its left, so replace it by -1.
For 5, 4 is the greatest element in its left.
For 2, 5 is the greatest element in its left.
For 1, 5 is the greatest element in its left.
For 7, 5 is the greatest element in its left.
For 6, 7 is the greatest element in its left.

Input: arr[] = {3, 2, 5, 7, 1}
Output: -1 3 3 5 7```

Approach:

1. Maintain a variable max_ele which will store the greatest element.
2. Initially, max_ele will be equal to the element at the 0th index.
3. First replace arr with -1 then traverse the array
4. And then replace the element with the max_ele value and update the max_ele if the element is greater than max_ele.
5. Print the modified array.

Below is the implementation of the above approach:

## C++

 `// C++ program to Replace every``// element with the greater element``// on its left side``#include ``using` `namespace` `std;` `// Function to replace the elements``void` `ReplaceElements(``int` `arr[], ``int` `n)``{``    ``// Max value initialised``    ``// to element at 0th index``    ``int` `max_ele = arr;``    ``arr = -1;` `    ``for` `(``int` `i = 1; i < n; ++i) {` `        ``// If max_ele is greater tha arr[i]``        ``// then just replace arr[i] with max_ele``        ``if` `(max_ele > arr[i])``            ``arr[i] = max_ele;` `        ``// Else if update the max_ele also``        ``else` `if` `(max_ele <= arr[i]) {``            ``int` `temp = arr[i];``            ``arr[i] = max_ele;``            ``max_ele = temp;``        ``}``    ``}``}` `// Driver code``int` `main()``{``    ``int` `arr[] = { 4, 5, 2, 1, 7, 6 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr);` `    ``// Replace the elements``    ``// with the smaller element``    ``// on its left side``    ``ReplaceElements(arr, n);` `    ``// Print the modified array``    ``for` `(``int` `i = 0; i < n; ++i)``        ``cout << arr[i] << ``" "``;` `    ``return` `0;``}`

## Java

 `// Java program to Replace every``// element with the greater element``// on its left side``import` `java.util.*;` `class` `Geeks {`  `// Function to replace the elements``static` `void` `ReplaceElements(``int` `arr[], ``int` `n)``{``    ``// Max value initialised``    ``// to element at 0th index``    ``int` `max_ele = arr[``0``];``    ``arr[``0``] = -``1``;` `    ``for` `(``int` `i = ``1``; i < n; ++i) {` `        ``// If max_ele is greater tha arr[i]``        ``// then just replace arr[i] with max_ele``        ``if` `(max_ele > arr[i])``            ``arr[i] = max_ele;` `        ``// Else if update the max_ele also``        ``else` `if` `(max_ele <= arr[i]) {``            ``int` `temp = arr[i];``            ``arr[i] = max_ele;``            ``max_ele = temp;``        ``}``    ``}``}` `// Driver code``public` `static` `void` `main(String args[])``{``    ``int` `arr[] = { ``4``, ``5``, ``2``, ``1``, ``7``, ``6` `};``    ``int` `n = arr.length;` `    ``// Replace the elements``    ``// with the smaller element``    ``// on its left side``    ``ReplaceElements(arr, n);` `    ``// Print the modified array``    ``for` `(``int` `i = ``0``; i < n; ++i)``        ``System.out.println(arr[i]);``}``}` `// This code is contributed by ankita_saini`

## Python3

 `# Python3 program to Replace every``# element with the greater element``# on its left side` `# Function to replace the elements``def` `ReplaceElements(arr, n):` `    ``# Max value initialised``    ``# to element at 0th index``    ``max_ele ``=` `arr[``0``]``    ``arr[``0``] ``=` `-``1` `    ``for` `i ``in` `range``(``1``, n):` `        ``# If max_ele is greater tha arr[i]``        ``# then just replace arr[i] with max_ele``        ``if` `(max_ele > arr[i]):``            ``arr[i] ``=` `max_ele` `        ``# Else if update the max_ele also``        ``elif` `(max_ele <``=` `arr[i]):``            ``temp ``=` `arr[i]``            ``arr[i] ``=` `max_ele``            ``max_ele ``=` `temp` `# Driver code``if` `__name__ ``=``=` `"__main__"``:` `    ``arr ``=` `[``4``, ``5``, ``2``, ``1``, ``7``, ``6` `]``    ``n ``=` `len``(arr)` `    ``# Replace the elements``    ``# with the smaller element``    ``# on its left side``    ``ReplaceElements(arr, n)` `    ``# Print the modified array``    ``for` `i ``in` `range` `(n):``        ``print``( arr[i], end ``=` `" "``)` `# This code is contributed``# by ChitraNayal`

## C#

 `// C# program to Replace every``// element with the greater element``// on its left side``using` `System;``public` `class` `GFG {` `// Function to replace the elements``static` `void` `ReplaceElements(``int` `[]arr, ``int` `n)``{``    ``// Max value initialised``    ``// to element at 0th index``    ``int` `max_ele = arr;``    ``arr = -1;` `    ``for` `(``int` `i = 1; i < n; ++i) {` `        ``// If max_ele is greater tha arr[i]``        ``// then just replace arr[i] with max_ele``        ``if` `(max_ele > arr[i])``            ``arr[i] = max_ele;` `        ``// Else if update the max_ele also``        ``else` `if` `(max_ele <= arr[i]) {``            ``int` `temp = arr[i];``            ``arr[i] = max_ele;``            ``max_ele = temp;``        ``}``    ``}``}` `// Driver code``public` `static` `void` `Main()``{``    ``int` `[]arr = { 4, 5, 2, 1, 7, 6 };``    ``int` `n = arr.Length;` `    ``// Replace the elements``    ``// with the smaller element``    ``// on its left side``    ``ReplaceElements(arr, n);` `    ``// Print the modified array``    ``for` `(``int` `i = 0; i < n; ++i) {``        ``Console.Write(arr[i]+``" "``);``    ``}``}``}` `// This code is contributed by Rajput-Ji`

## PHP

 ` ``\$arr``[``\$i``])``            ``\$arr``[``\$i``] = ``\$max_ele``;` `        ``// Else if update the max_ele also``        ``else` `if` `(``\$max_ele` `<= ``\$arr``[``\$i``])``        ``{``            ``\$temp` `= ``\$arr``[``\$i``];``            ``\$arr``[``\$i``] = ``\$max_ele``;``            ``\$max_ele` `= ``\$temp``;``        ``}``    ``}``    ``return` `\$arr``;``}` `// Driver code``\$arr` `= ``array``(4, 5, 2, 1, 7, 6);``\$n` `= sizeof(``\$arr``);` `// Replace the elements``// with the smaller element``// on its left side``\$arr1` `= ReplaceElements(``\$arr``, ``\$n``);` `// Print the modified array``for` `(``\$i` `= 0; ``\$i` `< ``\$n``; ++``\$i``)``    ``echo` `\$arr1``[``\$i``] . ``" "``;` `// This code is contributed``// by Akanksha Rai`

## Javascript

 ``
Output:

`-1 4 5 5 5 7`

Time Complexity: O(N)

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