Sorting all array elements except one

Last Updated : 29 Mar, 2024

Given an array, a positive integer, sort the array in ascending order such that the element at index K in the unsorted array stays unmoved and all other elements are sorted.

Examples:

Input : arr[] = {10, 4, 11, 7, 6, 20}
            k = 2;
Output : arr[] = {4, 6, 11, 7, 10, 20}

Input : arr[] = {30, 20, 10}
         k = 0
Output : arr[] = {30, 10, 20}

A simple solution is to copy all elements except k-th of a given array to another array. Then sort the other array using a sorting algorithm. Finally, again copy the sorted array to the original array. While copying, skip k-th element.

Below is an efficient solution.

Swap k-th element with the last element.
Sort all elements except the last.
For every element from (k+1)-th to last, move them one position ahead.1
Copy k-th element back to position k.

C++

// CPP program to sort all elements except 
// element at index k. 
#include <bits/stdc++.h> 
using namespace std; 
  
int sortExceptK(int arr[], int k, int n) 
{ 
    // Move k-th element to end 
    swap(arr[k], arr[n-1]); 
  
    // Sort all elements except last 
    sort(arr, arr + n - 1); 
  
    // Store last element (originally k-th) 
    int last = arr[n-1]; 
  
    // Move all elements from k-th to one 
    // position ahead. 
    for (int i=n-1; i>k; i--) 
       arr[i] = arr[i-1]; 
  
    // Restore k-th element 
    arr[k] = last; 
} 
  
// Driver code 
int main() 
{ 
    int a[] = {10, 4, 11, 7, 6, 20 }; 
    int k = 2; 
    int n = sizeof(a) / sizeof(a[0]); 
    sortExceptK(a, k, n); 
    for (int i = 0; i < n; i++) 
        cout << a[i] << " "; 
} 

Java

// Java program to sort all elements except 
// element at index k. 
import java.util.Arrays; 
  
class GFG { 
      
    static int sortExceptK(int arr[], int k, int n) 
    { 
          
        // Move k-th element to end 
        int temp = arr[k]; 
        arr[k] = arr[n-1]; 
        arr[n-1] = temp; 
      
        // Sort all elements except last 
        Arrays.sort(arr, 0, n-1); 
      
        // Store last element (originally k-th) 
        int last = arr[n-1]; 
      
        // Move all elements from k-th to one 
        // position ahead. 
        for (int i = n-1; i > k; i--) 
        arr[i] = arr[i-1]; 
      
        // Restore k-th element 
        arr[k] = last; 
        return 0; 
    } 
      
    //Driver code 
    public static void main (String[] args) 
    { 
        int a[] = {10, 4, 11, 7, 6, 20 }; 
        int k = 2; 
        int n = a.length; 
          
        sortExceptK(a, k, n); 
          
        for (int i = 0; i < n; i++) 
            System.out.print(a[i] + " "); 
    } 
} 
  
//This code is contributed by Anant Agarwal. 

Python3

# Python3 program to sort all elements except 
# element at index k. 
def sortExcept(arr, k, n): 
  
    # Move k-th element to end 
    arr[k], arr[-1] = arr[-1], arr[k] 
  
    # Sort all elements except last 
    arr = sorted(arr, key = lambda i: (i is arr[-1], i)) 
      
    # Store last element (originally k-th) 
    last = arr[-1] 
  
    # Move all elements from k-th to one 
    # position ahead. 
    i = n - 1
    while i > k: 
        arr[i] = arr[i - 1] 
        i -= 1
  
    # Restore k-th element 
    arr[k] = last 
    return arr 
  
# Driver code 
if __name__ == '__main__': 
    a = [10, 4, 11, 7, 6, 20] 
    k = 2
    n = len(a) 
    a = sortExcept(a, k, n) 
    print(" ".join(list(map(str, a)))) 
      
# This code is contributed by Shivam Singh. 

C#

// C# program to sort all elements except 
// element at index k. 
using System; 
  
public class GFG { 
      
    static int sortExceptK(int[] arr, int k, int n) 
    { 
        // Move k-th element to end 
        int temp = arr[k]; 
        arr[k] = arr[n - 1]; 
        arr[n - 1] = temp; 
  
        // Sort all elements except last 
        Array.Sort(arr, 0, n - 1); 
  
        // Store last element (originally k-th) 
        int last = arr[n - 1]; 
  
        // Move all elements from k-th to one 
        // position ahead. 
        for (int i = n - 1; i > k; i--) 
            arr[i] = arr[i - 1]; 
  
        // Restore k-th element 
        arr[k] = last; 
          
        return 0; 
    } 
      
    // Driver code 
    public static void Main() 
    { 
        int[] a = { 10, 4, 11, 7, 6, 20 }; 
        int k = 2; 
        int n = a.Length; 
  
        sortExceptK(a, k, n); 
  
        for (int i = 0; i < n; i++) 
        Console.Write(a[i] + " "); 
    } 
} 
  
// This article is contributed by shiv_bhakt 

PHP

<?php 
// PHP program to sort all  
// elements except element 
// at index k. 
function sortExceptK(&$arr, $k, $n) 
{ 
    // Move k-th element to end 
    $t = $arr[$k]; 
    $arr[$k] = $arr[$n - 1]; 
    $arr[$n - 1] = $t; 
  
    // Sort all elements  
    // except last 
    $t = $arr[count($arr) - 1]; 
    $arr = array_slice($arr, 0, -1); 
    sort($arr); 
    array_push($arr, $t); 
  
    // Store last element 
    // (originally k-th) 
    $last = $arr[$n - 1]; 
  
    // Move all elements from  
    // k-th to one position ahead. 
    for ($i = $n - 1; $i > $k; $i--) 
    $arr[$i] = $arr[$i - 1]; 
  
    // Restore k-th element 
    $arr[$k] = $last; 
} 
  
// Driver code 
$a = array(10, 4, 11,  
            7, 6, 20 ); 
$k = 2; 
$n = count($a); 
sortExceptK($a, $k, $n); 
  
for ($i = 0; $i < $n; $i++) 
    echo ($a[$i]." "); 
      
// This code is contributed by  
// Manish Shaw(manishshaw1) 
?> 

Javascript

<script> 
    // Javascript program to sort all elements except 
    // element at index k. 
      
    function sortExceptK(arr, k, n) 
    { 
            
        // Move k-th element to end 
        let temp = arr[k]; 
        arr[k] = arr[n-1]; 
        arr[n-1] = temp; 
        
        // Sort all elements except last 
        arr.sort(function(a, b){ 
            return a - b}); 
        
        // Store last element (originally k-th) 
        let last = arr[n-1]; 
        
        // Move all elements from k-th to one 
        // position ahead. 
        for (let i = n-1; i > k; i--) 
            arr[i] = arr[i-1]; 
        
        // Restore k-th element 
        arr[k] = last; 
          
        // Move k-th element to end 
        temp = arr[k]; 
        arr[k] = arr[n-1]; 
        arr[n-1] = temp; 
          
        return 0; 
    } 
      
    let a = [10, 4, 11, 7, 6, 20 ]; 
    let k = 2; 
    let n = a.length; 
  
    sortExceptK(a, k, n); 
  
    for(let i = 0; i < n; i++) 
      document.write(a[i] + " "); 
  
</script>