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Minimum flips or swapping of adjacent characters required to make a string equal to another
  • Last Updated : 18 Jun, 2021

Given two binary strings A and B of length N, the task is to convert the string A to B by either flipping any character of A or swapping adjacent characters of A minimum number of times. If it is not possible to make both the strings equal, print -1.

Examples:

Input: A = “10010010”, B = “00001000”  
Output: 3
Explanation:
Operation 1: Flipping A[0] modifies A to “00010010”.
Operation 2: Flipping A[6] modifies A to “00010000”.
Operation 3: Swapping A[3] and A[4] modifies A to “00001000” 
Therefore, the total number of operations is 3.

Input: A = “11”, B = “00”  
Output: 3

Approach: The idea is to traverse the string A and try to make the same-indexed characters equal by first checking for the condition of swapping the adjacent characters. If the characters can not be made equal by this operation, then flip the character. Follow the steps below to solve the problem:



  • Initialize a variable, say ans, to store the required result.
  • Traverse the string A using a variable, say i, and perform the following operations:
  • Print the value of ans as the result.

Below is the implementation of the above approach:

C++




// C++ program for the above approach
#include <bits/stdc++.h>
using namespace std;
 
// Function to find minimum operations
// required to convert string A to B
int minimumOperation(string a, string b)
{
 
    // Store the size of the string
    int n = a.length();
    int i = 0;
 
    // Store the required result
    int minoperation = 0;
 
    // Traverse the string, a
    while (i < n) {
 
        // If a[i] is equal to b[i]
        if (a[i] == b[i]) {
            i = i + 1;
            continue;
        }
 
        // Check if swapping adjacent
        // characters make the same-indexed
        // characters equal or not
        else if (a[i] == b[i + 1]
                 && a[i + 1] == b[i]
                 && i < n - 1) {
 
            minoperation++;
            i = i + 2;
        }
 
        // Otherwise, flip the current bit
        else if (a[i] != b[i]) {
            minoperation++;
            i = i + 1;
        }
        else {
            ++i;
        }
    }
 
    // Print the minimum number of operations
    cout << minoperation;
}
 
// Driver Code
int main()
{
    // Given Input
    string a = "10010010", b = "00001000";
 
    // Function Call
    minimumOperation(a, b);
 
    return 0;
}

Java




// Java program for the above approach
public class GFG
{
     
// Function to find minimum operations
// required to convert string A to B
static void minimumOperation(String a, String b)
{
     
    // Store the size of the string
    int n = a.length();
    int i = 0;
 
    // Store the required result
    int minoperation = 0;
 
    // Traverse the string, a
    while (i < n)
    {
         
        // If a[i] is equal to b[i]
        if (a.charAt(i) == b.charAt(i))
        {
            i = i + 1;
            continue;
        }
 
        // Check if swapping adjacent
        // characters make the same-indexed
        // characters equal or not
        else if (a.charAt(i) == b.charAt(i + 1) && 
                 a.charAt(i + 1) == b.charAt(i) &&
                   i < n - 1)
        {
            minoperation++;
            i = i + 2;
        }
 
        // Otherwise, flip the current bit
        else if (a.charAt(i) != b.charAt(i))
        {
            minoperation++;
            i = i + 1;
        }
        else
        {
            ++i;
        }
    }
 
    // Print the minimum number of operations
    System.out.println(minoperation);
}
 
// Driver Code
public static void main(String []args)
{
     
    // Given Input
    String a = "10010010", b = "00001000";
 
    // Function Call
    minimumOperation(a, b);
}
}
 
// This code is contributed by AnkThon

Python3




# Python3 program for the above approach
 
# Function to find minimum operations
# required to convert A to B
def minimumOperation(a, b):
 
    # Store the size of the string
    n = len(a)
    i = 0
 
    # Store the required result
    minoperation = 0
 
    # Traverse the string, a
    while (i < n):
 
        # If a[i] is equal to b[i]
        if (a[i] == b[i]):
            i = i + 1
            continue
 
        # Check if swapping adjacent
        # characters make the same-indexed
        # characters equal or not
        elif (a[i] == b[i + 1] and
              a[i + 1] == b[i] and i < n - 1):
            minoperation += 1
            i = i + 2
 
        # Otherwise, flip the current bit
        elif (a[i] != b[i]):
            minoperation += 1
            i = i + 1
        else:
            i+=1
 
    # Print the minimum number of operations
    print (minoperation)
 
# Driver Code
if __name__ == '__main__':
     
    # Given Input
    a = "10010010"
    b = "00001000"
 
    # Function Call
    minimumOperation(a, b)
     
# This code is contributed by mohit kumar 29

C#




// C# program for the above approach
using System;
 
class GFG{
     
// Function to find minimum operations
// required to convert string A to B
static void minimumOperation(string a, string b)
{
     
    // Store the size of the string
    int n = a.Length;
    int i = 0;
 
    // Store the required result
    int minoperation = 0;
 
    // Traverse the string, a
    while (i < n)
    {
         
        // If a[i] is equal to b[i]
        if (a[i] == b[i])
        {
            i = i + 1;
            continue;
        }
 
        // Check if swapping adjacent
        // characters make the same-indexed
        // characters equal or not
        else if (a[i] == b[i + 1] && 
                 a[i + 1] == b[i] &&
                   i < n - 1)
        {
            minoperation++;
            i = i + 2;
        }
 
        // Otherwise, flip the current bit
        else if (a[i] != b[i])
        {
            minoperation++;
            i = i + 1;
        }
        else
        {
            ++i;
        }
    }
 
    // Print the minimum number of operations
    Console.WriteLine(minoperation);
}
 
// Driver Code
public static void Main()
{
     
    // Given Input
    string a = "10010010", b = "00001000";
 
    // Function Call
    minimumOperation(a, b);
}
}
 
// This code is contributed by ankThon

Javascript




<script>
 
// Javascript program for the above approach
 
// Function to find minimum operations
// required to convert string A to B
function minimumOperation(a, b)
{
 
    // Store the size of the string
    var n = a.length;
    var i = 0;
 
    // Store the required result
    var minoperation = 0;
 
    // Traverse the string, a
    while (i < n) {
 
        // If a[i] is equal to b[i]
        if (a[i] == b[i]) {
            i = i + 1;
            continue;
        }
 
        // Check if swapping adjacent
        // characters make the same-indexed
        // characters equal or not
        else if (a[i] == b[i + 1]
                 && a[i + 1] == b[i]
                 && i < n - 1) {
 
            minoperation++;
            i = i + 2;
        }
 
        // Otherwise, flip the current bit
        else if (a[i] != b[i]) {
            minoperation++;
            i = i + 1;
        }
        else {
            ++i;
        }
    }
 
    // Print the minimum number of operations
    document.write(minoperation);
}
 
// Driver Code
 
    // Given Input
    var a = "10010010", b = "00001000";
 
    // Function Call
    minimumOperation(a, b);
     
</script>
Output: 
3

 

Time Complexity: O(N)
Auxiliary Space: O(1)

 

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