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Minimum swaps to make two strings equal by swapping only with third string

  • Last Updated : 14 May, 2021

Given three strings A, B, and C of equal length, the task is to find the minimum number of swap operations that can be performed such that the strings A and B become equal when any swapping can be done only with C.

Examples: 

Input: A = “xyz”, B = “yzx”, C = “yzx” 
Output:
Explanation: 
Swap all the characters of string C with string A one by one
Input: A = “pqr”, B = “stu”, C = “vwx” 
Output: -1 
Explanation 
It’s impossible to make strings A and B equal, even by using C  

Approach: Since the lengths of the strings are equal, the idea is to traverse the strings and check for the characters present in the strings. 
For every index ‘i’, the following cases occur:  

  1. If the character at the given index for the string A is the same as the character in B, then we can proceed to check the next character.
  2. If the character at the given index for the string A and B are not equal, then we check if the character at strings B and C or A and C are equal, and accordingly, we swap those characters.
  3. If none of the above conditions satisfies, then it’s impossible to make the strings A and B equal.

Below is the implementation of the above approach:  

C++




// C++ implementation to find the
// minimum number of swaps to make
// two strings equal
 
#include <bits/stdc++.h>
using namespace std;
 
// Function to swap the characters
void swap(char& x, char& y)
{
    char temp = x;
    x = y;
    y = temp;
}
 
// Function to find the minimum number of swaps
// to make two strings equal
void swapOperations(string a, string b, string c)
{
    // Counting length of string
    int l = a.length();
    int i = 0;
 
    // Initializing the answer
    int total_swaps = 0;
 
    // For loop to iterate through the
    // given strings
    for (i = 0; i < l; i++) {
 
        // Condition if both character of
        // string a and b are equal
        if (a[i] == b[i])
            continue;
 
        // Condition if character of
        // string a and c are equal
        if (a[i] == c[i]) {
 
            // If yes, then swap
            // the characters
            swap(b[i], c[i]);
            total_swaps++;
            continue;
        }
 
        // Condition if character of
        // string b and c are equal
        if (b[i] == c[i]) {
 
            // If yes, then swap
            // the characters
            swap(a[i], c[i]);
            total_swaps++;
            continue;
        }
 
        // Else, it is impossible to make
        // both the strings equal
        break;
    }
 
    // Printing the answer
    if (i == l)
        cout << total_swaps << endl;
    else
        cout << -1 << endl;
}
 
// Driver Code
int main()
{
    string a = "xyz";
    string b = "yzx";
    string c = "yzx";
 
    swapOperations(a, b, c);
 
    return 0;
}

Java




// Java implementation to find the
// minimum number of swaps to make
// two strings equal
class GFG {
     
    // Function to find the minimum number of swaps
    // to make two strings equal
    static void swapOperations(char []a, char []b, char []c)
    {
        // Counting length of string
        int l = a.length;
        int i = 0;
     
        // Initializing the answer
        int total_swaps = 0;
        char temp;
     
        // For loop to iterate through the
        // given strings
        for (i = 0; i < l; i++) {
     
            // Condition if both character of
            // string a and b are equal
            if (a[i] == b[i])
                continue;
     
            // Condition if character of
            // string a and c are equal
            if (a[i] == c[i]) {
     
                // If yes, then swap
                // the characters
                //    swap(b[i], c[i]);
                temp = b[i];
                b[i] = c[i];
                c[i] = temp;
                 
                total_swaps++;
                continue;
            }
     
            // Condition if character of
            // string b and c are equal
            if (b[i] == c[i]) {
     
                // If yes, then swap
                // the characters
                //swap(a[i], c[i]);
                temp = a[i];
                a[i] = c[i];
                c[i] = temp;
                 
                total_swaps++;
                continue;
            }
     
            // Else, it is impossible to make
            // both the strings equal
            break;
        }
     
        // Printing the answer
        if (i == l)
                System.out.println(total_swaps) ;
        else
                System.out.println(-1) ;
    }
     
    // Driver Code
    public static void main (String[] args)
    {
        String a = "xyz";
        String b = "yzx";
        String c = "yzx";
     
        swapOperations(a.toCharArray(), b.toCharArray(), c.toCharArray());
     
    }
}
 
// This code is contributed by Yash_R

Python3




# Python3 implementation to find the
# minimum number of swaps to make
# two strings equal
 
# Function to find the minimum number of swaps
# to make two strings equal
def swapOperations(a, b, c) :
 
    # Counting length of string
    l = len(a);
    i = 0;
 
    # Initializing the answer
    total_swaps = 0;
 
    # For loop to iterate through the
    # given strings
    for i in range(l) :
 
        # Condition if both character of
        # string a and b are equal
        if (a[i] == b[i]) :
            continue;
 
        # Condition if character of
        # string a and c are equal
        if (a[i] == c[i]) :
 
            # If yes, then swap
            # the characters
            #swap(b[i], c[i]);
            b[i], c[i] = c[i], b[i];
            total_swaps += 1;
            continue;
 
        # Condition if character of
        # string b and c are equal
        if (b[i] == c[i]) :
 
            # If yes, then swap
            # the characters
            # swap(a[i], c[i]);
            a[i], c[i] = c[i], a[i];
            total_swaps += 1;
            continue;
 
        # Else, it is impossible to make
        # both the strings equal
        break;
     
    i += 1;
 
    # Printing the answer
    if (i == l) :
        print(total_swaps) ;
    else :
        print(-1);
 
# Driver Code
if __name__ == "__main__" :
 
    a = "xyz";
    b = "yzx";
    c = "yzx";
 
    swapOperations(list(a), list(b), list(c));
 
# This code is contributed by AnkitRai01

C#




// C# implementation to find the
// minimum number of swaps to make
// two strings equal
using System;
 
class GFG {
     
    // Function to find the minimum number of swaps
    // to make two strings equal
    static void swapOperations(char []a, char []b, char []c)
    {
        // Counting length of string
        int l = a.Length;
        int i = 0;
     
        // Initializing the answer
        int total_swaps = 0;
        char temp;
     
        // For loop to iterate through the
        // given strings
        for (i = 0; i < l; i++) {
     
            // Condition if both character of
            // string a and b are equal
            if (a[i] == b[i])
                continue;
     
            // Condition if character of
            // string a and c are equal
            if (a[i] == c[i]) {
     
                // If yes, then swap
                // the characters
                //    swap(b[i], c[i]);
                temp = b[i];
                b[i] = c[i];
                c[i] = temp;
                 
                total_swaps++;
                continue;
            }
     
            // Condition if character of
            // string b and c are equal
            if (b[i] == c[i]) {
     
                // If yes, then swap
                // the characters
                //swap(a[i], c[i]);
                temp = a[i];
                a[i] = c[i];
                c[i] = temp;
                 
                total_swaps++;
                continue;
            }
     
            // Else, it is impossible to make
            // both the strings equal
            break;
        }
     
        // Printing the answer
        if (i == l)
                Console.WriteLine(total_swaps) ;
        else
                Console.WriteLine(-1) ;
    }
     
    // Driver Code
    public static void Main(string[] args)
    {
        string a = "xyz";
        string b = "yzx";
        string c = "yzx";
     
        swapOperations(a.ToCharArray(), b.ToCharArray(), c.ToCharArray());
     
    }
}
 
// This code is contributed by Yash_R

Javascript




<script>
      // JavaScript implementation to find the
      // minimum number of swaps to make
      // two strings equal
      // Function to find the minimum number of swaps
      // to make two strings equal
      function swapOperations(a, b, c) {
        // Counting length of string
        var l = a.length;
        var i = 0;
 
        // Initializing the answer
        var total_swaps = 0;
 
        // For loop to iterate through the
        // given strings
        for (i = 0; i < l; i++) {
          // Condition if both character of
          // string a and b are equal
          if (a[i] === b[i]) continue;
 
          // Condition if character of
          // string a and c are equal
          if (a[i] === c[i]) {
            // If yes, then swap
            // the characters
            // swap(b[i], c[i]);
            var temp = b[i];
            b[i] = c[i];
            c[i] = temp;
 
            total_swaps++;
            continue;
          }
 
          // Condition if character of
          // string b and c are equal
          if (b[i] === c[i]) {
            // If yes, then swap
            // the characters
            //swap(a[i], c[i]);
            var temp = a[i];
            a[i] = c[i];
            c[i] = temp;
 
            total_swaps++;
            continue;
          }
 
          // Else, it is impossible to make
          // both the strings equal
          break;
        }
 
        // Printing the answer
        if (i === l) document.write(total_swaps);
        else document.write(-1);
      }
 
      // Driver Code
      var a = "xyz";
      var b = "yzx";
      var c = "yzx";
 
      swapOperations(a.split(""), b.split(""), c.split(""));
    </script>
Output: 
3

 

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