Generate permutations with only adjacent swaps allowed - GeeksforGeeks

16 Jun, 2021
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++
Java
Python3
C#
PHP
Javascript
// 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 codeint main(){    char str[] = { "12345" };    int n = strlen(str);    findPermutations(str, 0, n);    return 0;}
// 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
# Python3 program to generate permutations# with only one swap allowed.def findPermutations(string, index, n):    if index >= n or (index + 1) >= n:        print(''.join(string))        return     # don't swap the current position    findPermutations(string, 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.    string[index], \    string[index + 1] = string[index + 1], \                        string[index]                             findPermutations(string, index + 2, n)         string[index], \    string[index + 1] = string[index + 1], \                        string[index] # Driver Codeif __name__ == "__main__":    string = list("12345")    n = len(string)    findPermutations(string, 0, n) # This code is contributed by# sanjeev2552
// 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
<?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?>
<script>       // JavaScript program to generate      // permutations with only      // one swap allowed.      function findPermutations(str, index, n) {        if (index >= n || index + 1 >= n) {          document.write(str.join("") + "<br>");          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);      }       function swap(arr, index) {        var temp = arr[index];        arr[index] = arr[index + 1];        arr[index + 1] = temp;      }      // Driver code       var str = "12345".split("");      var n = str.length;      findPermutations(str, 0, n);       </script>
Output:  
12345
12354
12435
13245
13254
21345
21354
21435
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Sach_Code
29AjayKumar
Rajput-Ji
sanjeev2552
rdtank
Goldman Sachs
Combinatorial
Strings
Goldman Sachs
Strings
Combinatorial
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