Generate permutations with only adjacent swaps allowed

Given a string on length N. You can swap only the adjacent elements and each element can be swapped atmost once. Find the no of permutations of the string that can be generated after performing the swaps as mentioned.

Examples:

Input : 12345
Output : 12345 12354 12435 13245 13254 
         21345 21354 21435

Source: Goldman Sachs Interview

Consider any i-th character in the string. There are two possibilities for this character:
1.) Don’t swap it, i.e. don’t do anything with this character and move to the next character.
2.) Swap it. As it can be swapped with its adjacent,
……..a.) Swap it with the next character. Because each character can be swapped atmost once, we’ll move to the position (i+2).
……. b.) Swap it with the previous character – we don’t need to consider this case separately as i-th character is the next character of (i-1)th which is same as the case 2.a.

C++

filter_none

edit
close

play_arrow

link
brightness_4
code

// CPP program to generate permutations with only
// one swap allowed.
#include <cstring>
#include <iostream>
using namespace std;
  
void findPermutations(char str[], int index, int n)
{
    if (index >= n || (index + 1) >= n) {
        cout << str << endl;
        return;
    }
  
    // don't swap the current position
    findPermutations(str, index + 1, n);
  
    // Swap with the next character and
    // revert the changes. As explained
    // above, swapping with previous is
    // is not needed as it anyways happens
    // for next character.
    swap(str[index], str[index + 1]);
    findPermutations(str, index + 2, n);
    swap(str[index], str[index + 1]);
}
  
// Driver code
int main()
{
    char str[] = { "12345" };
    int n = strlen(str);
    findPermutations(str, 0, n);
    return 0;
}

chevron_right


Java

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java program to generate permutations with only
// one swap allowed.
  
class GFG {
  
    static void findPermutations(char str[], int index, int n) {
        if (index >= n || (index + 1) >= n) {
            System.out.println(str);
            return;
        }
  
        // don't swap the current position
        findPermutations(str, index + 1, n);
  
        // Swap with the next character and
        // revert the changes. As explained
        // above, swapping with previous is
        // is not needed as it anyways happens
        // for next character.
        swap(str, index);
        findPermutations(str, index + 2, n);
        swap(str, index);
    }
  
    static void swap(char arr[], int index) {
        char temp = arr[index];
        arr[index] = arr[index + 1];
        arr[index + 1] = temp;
    }
// Driver code
  
    public static void main(String[] args) {
        char str[] = "12345".toCharArray();
        int n = str.length;
        findPermutations(str, 0, n);
    }
}
// This code is contributed by 29AjayKumar

chevron_right


C#

filter_none

edit
close

play_arrow

link
brightness_4
code

// C# program to generate permutations with only 
// one swap allowed. 
using System; 
public class GFG { 
  
    static void findPermutations(char []str, int index, int n) { 
        if (index >= n || (index + 1) >= n) { 
            Console.WriteLine(str); 
            return
        
  
        // don't swap the current position 
        findPermutations(str, index + 1, n); 
  
        // Swap with the next character and 
        // revert the changes. As explained 
        // above, swapping with previous is 
        // is not needed as it anyways happens 
        // for next character. 
        swap(str, index); 
        findPermutations(str, index + 2, n); 
        swap(str, index); 
    
  
    static void swap(char []arr, int index) { 
        char temp = arr[index]; 
        arr[index] = arr[index + 1]; 
        arr[index + 1] = temp; 
    
// Driver code 
  
    public static void Main() { 
        char []str = "12345".ToCharArray(); 
        int n = str.Length; 
        findPermutations(str, 0, n); 
    
  
// This code is contributed by Rajput-Ji

chevron_right


PHP

filter_none

edit
close

play_arrow

link
brightness_4
code

<?php
// PHP program to generate permutations
// with only one swap allowed. 
  
function findPermutations($str, $index, $n
    if ($index >= $n || ($index + 1) >= $n
    
        echo $str, "\n"
        return
    
  
    // don't swap the current position 
    findPermutations($str, $index + 1, $n); 
  
    // Swap with the next character and 
    // revert the changes. As explained 
    // above, swapping with previous is 
    // is not needed as it anyways happens 
    // for next character. 
    list($str[$index], 
         $str[$index + 1]) = array($str[$index + 1], 
                                   $str[$index]);
  
    findPermutations($str, $index + 2, $n); 
    list($str[$index], 
         $str[$index + 1]) = array($str[$index + 1],
                                   $str[$index]);
  
// Driver code 
$str = "12345"
$n = strlen($str); 
findPermutations($str, 0, $n); 
  
// This code is contributed by Sach_Code
?>

chevron_right



Output:

12345
12354
12435
13245
13254
21345
21354
21435

This article is contributed by ekta1994. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.



My Personal Notes arrow_drop_up