Sort an array with swapping only with a special element is allowed

Given an array of length n + 1, containing elements 1 through n and a space, Requires the use of a given swap (index i, index j) function to sort the array, You can only swap the gap and a number, in the end, put the gap at the end.
There will be a number 999 in array as gap or space.
Examples:

Input  : arr = {1, 5, 4, 999, 3, 2}
Output : arr = {1, 2, 3, 4, 5, 999}
We need to sort only by moving 

Input  : arr = {1, 5, 4, 3, 2, 8, 7, 999, 6}
Output : arr = {1, 2, 3, 4, 5, 6, 7, 8, 999}

We follow a recursive approach to solve this problem. As we can only swap numbers with the space. First of all we find the index of space. If the index is start of array, then move this space to the second last index by swapping with each number in it’s right.
If space is neither start of array nor last element of array and element before it greater than the element next to space then do following.

Step 1: Swap space and element next to space
In case of {3, 999, 2} make it {3, 2, 999}



Step 2 : Swap space and greater element
eg-convert {3, 2, 999} to {999, 2, 3}

Otherwise, elements next to index are sorted and swap it with the previous element. Again call the sort function with size of array decreased by 1 and index of space – 1 as we will get one sorted element each time.

C++

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// CPP program to sort an array by moving one
// space around.
#include <bits/stdc++.h>
using namespace std;
  
// n is total number of elements.
// index is index of 999 or space.
// k is number of elements yet to be sorted.
void sortRec(int arr[], int index, int k, int n)
{
    // print the sorted array when loop reaches
    // the base case
    if (k == 0) {
        for (int i = 1; i < n; i++)
            cout << arr[i] << " ";
        cout << 999;
        return;
    }
  
    // else if k>0 and space is at 0th index swap
    // each number with space and store index at
    // second last index
    else if (k > 0 && index == 0) {
        index = n - 2;
        for (int i = 1; i <= index; i++) {
            arr[i - 1] = arr[i];
        }
        arr[index] = 999;
    }
  
    // if space is neither start of array nor last
    // element of array and element before it greater
    // than/ the element next to space
    if (index - 1 >= 0 && index + 1 < n && 
       arr[index - 1] > arr[index + 1]) {
  
        // first swap space and element next to space
        // in case of {3, 999, 2} make it {3, 2, 999}
        swap(arr[index], arr[index + 1]);
  
        // than swap space and greater element
        // convert {3, 2, 999} to {999, 2, 3}
        swap(arr[index - 1], arr[index + 1]);
    }
  
    else
        swap(arr[index], arr[index - 1]);
  
    sortRec(arr, index - 1, k - 1, n);
}
  
// Wrapper over sortRec.
void sort(int arr[], int n)
{
    // Find index of space (or 999)
    int index = -1;
    for (int i = 0; i < n; i++) {
        if (arr[i] == 999) {
            index = i;
            break;
        }
    }
  
    // Invalid input
    if (index == -1)
        return;
  
    sortRec(arr, index, n, n);
}
  
  
// driver program
int main()
{
    int arr[] = { 3, 2, 999, 1 };
    int n = sizeof(arr) / sizeof(arr[0]);
    sort(arr, n);
    return 0;
}

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Java

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// Java program to sort an array by moving one 
// space around. 
  
class GFG
{
  
// n is total number of elements. 
// index is index of 999 or space. 
// k is number of elements yet to be sorted. 
static void sortRec(int arr[], int index, int k, int n) 
    // print the sorted array when loop reaches 
    // the base case 
    if (k == 0)
    
        for (int i = 1; i < n; i++) 
                        System.out.print(arr[i] + " "); 
                System.out.println(999); 
        return
    
  
    // else if k>0 and space is at 0th index swap 
    // each number with space and store index at 
    // second last index 
    else if (k > 0 && index == 0)
    
        index = n - 2
        for (int i = 1; i <= index; i++)
        
            arr[i - 1] = arr[i]; 
        
        arr[index] = 999
    
  
    // if space is neither start of array nor last 
    // element of array and element before it greater 
    // than/ the element next to space 
    if (index - 1 >= 0 && index + 1 < n && 
    arr[index - 1] > arr[index + 1])
    
  
        // first swap space and element next to space 
        // in case of {3, 999, 2} make it {3, 2, 999} 
        swap(arr,index, index + 1); 
  
        // than swap space and greater element 
        // convert {3, 2, 999} to {999, 2, 3} 
        swap(arr,index - 1, index + 1); 
    
  
    else
        swap(arr,index, index - 1); 
  
    sortRec(arr, index - 1, k - 1, n); 
  
static int[] swap(int []arr, int i, int j)
{
    int temp = arr[i];
    arr[i] = arr[j];
    arr[j] = temp;
    return arr;
}
  
// Wrapper over sortRec. 
static void sort(int arr[], int n) 
    // Find index of space (or 999) 
    int index = -1
    for (int i = 0; i < n; i++)
    
        if (arr[i] == 999)
        
            index = i; 
            break
        
    
  
    // Invalid input 
    if (index == -1
        return
  
    sortRec(arr, index, n, n); 
  
  
// Driver code 
public static void main(String[] args)
{
    int arr[] = { 3, 2, 999, 1 }; 
    int n = arr.length; 
    sort(arr, n); 
}
}
  
// This code contributed by Rajput-Ji

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C#

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// C# program to sort an array by moving one 
// space around. 
using System;
  
class GFG 
  
// n is total number of elements. 
// index is index of 999 or space. 
// k is number of elements yet to be sorted. 
static void sortRec(int []arr, int index, int k, int n) 
    // print the sorted array when loop reaches 
    // the base case 
    if (k == 0) 
    
        for (int i = 1; i < n; i++) 
                        Console.Write(arr[i] + " "); 
                Console.WriteLine(999); 
        return
    
  
    // else if k>0 and space is at 0th index swap 
    // each number with space and store index at 
    // second last index 
    else if (k > 0 && index == 0) 
    
        index = n - 2; 
        for (int i = 1; i <= index; i++) 
        
            arr[i - 1] = arr[i]; 
        
        arr[index] = 999; 
    
  
    // if space is neither start of array nor last 
    // element of array and element before it greater 
    // than/ the element next to space 
    if (index - 1 >= 0 && index + 1 < n && 
    arr[index - 1] > arr[index + 1]) 
    
  
        // first swap space and element next to space 
        // in case of {3, 999, 2} make it {3, 2, 999} 
        swap(arr,index, index + 1); 
  
        // than swap space and greater element 
        // convert {3, 2, 999} to {999, 2, 3} 
        swap(arr,index - 1, index + 1); 
    
  
    else
        swap(arr,index, index - 1); 
  
    sortRec(arr, index - 1, k - 1, n); 
  
static int[] swap(int []arr, int i, int j) 
    int temp = arr[i]; 
    arr[i] = arr[j]; 
    arr[j] = temp; 
    return arr; 
  
// Wrapper over sortRec. 
static void sort(int []arr, int n) 
    // Find index of space (or 999) 
    int index = -1; 
    for (int i = 0; i < n; i++) 
    
        if (arr[i] == 999) 
        
            index = i; 
            break
        
    
  
    // Invalid input 
    if (index == -1) 
        return
  
    sortRec(arr, index, n, n); 
  
  
// Driver code 
public static void Main(String[] args) 
    int []arr = { 3, 2, 999, 1 }; 
    int n = arr.Length; 
    sort(arr, n); 
  
// This code has been contributed by 29AjayKumar

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Output:

1 2 3 999

Time Complexity- O(n2)



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Improved By : Rajput-Ji, 29AjayKumar



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