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Minimum move to end operations to make all strings equal
  • Difficulty Level : Medium
  • Last Updated : 03 May, 2021

Given n strings that are permutations of each other. We need to make all strings same with an operation that takes front character of any string and moves it to the end.
Examples: 
 

Input : n = 2
        arr[] = {"molzv", "lzvmo"}
Output : 2
Explanation: In first string, we remove
first element("m") from first string and 
append it end. Then we move second character
of first string and move it to end. So after
2 operations, both strings become same.

Input : n = 3
        arr[] = {"kc", "kc", "kc"}
Output : 0
Explanation: already all strings are equal.

 

The move to end operation is basically left rotation. We use the approach discussed in check if strings are rotations of each other or not to count number of move to front operations required to make two strings same. We one by one consider every string as the target string. We count rotations required to make all other strings same as current target and finally return minimum of all counts.
Below is the implementation of above approach. 
 

C++




// CPP program to make all strings same using
// move to end operations.
#include <bits/stdc++.h>
using namespace std;
 
// Returns minimum number of moves to end
// operations to make all strings same.
int minimunMoves(string arr[], int n)
{
    int ans = INT_MAX;
    for (int i = 0; i < n; i++)
    {
        int curr_count = 0; 
 
        // Consider s[i] as target string and
        // count rotations required to make
        // all other strings same as str[i].
        for (int j = 0; j < n; j++) {
 
            string tmp = arr[j] + arr[j];
 
            // find function returns the index where we
            // found arr[i] which is actually count of
            // move-to-front operations.
            int index = tmp.find(arr[i]);
 
            // If any two strings are not rotations of
            // each other, we can't make them same. 
            if (index == string::npos)
                return -1;
 
            curr_count += index;
        }
 
        ans = min(curr_count, ans);
    }
 
    return ans;
}
 
// driver code for above function.
int main()
{
    string arr[] = {"xzzwo", "zwoxz", "zzwox", "xzzwo"}; 
    int n = sizeof(arr)/sizeof(arr[0]);
    cout << minimunMoves(arr, n);
    return 0;
}

Java




// Java program to make all
// strings same using move
// to end operations.
import java.util.*;
class GFG
{
 
// Returns minimum number of
// moves to end operations
// to make all strings same.
static int minimunMoves(String arr[], int n)
{
    int ans = Integer.MAX_VALUE;
    for (int i = 0; i < n; i++)
    {
        int curr_count = 0;
 
        // Consider s[i] as target
        // string and count rotations
        // required to make all other
        // strings same as str[i].
        String tmp = "";
        for (int j = 0; j < n; j++)
        {
            tmp = arr[j] + arr[j];
 
            // find function returns the
            // index where we found arr[i]
            // which is actually count of
            // move-to-front operations.
            int index = tmp.indexOf(arr[i]);
 
            // If any two strings are not
            // rotations of each other,
            // we can't make them same.
            if (index == arr[i].length())
                return -1;
                 
            curr_count += index;
        }
 
        ans = Math.min(curr_count, ans);
    }
 
    return ans;
}
 
// Driver code
public static void main(String args[])
{
    String arr[] = {"xzzwo", "zwoxz",
                    "zzwox", "xzzwo"};
    int n = arr.length;
    System.out.println(minimunMoves(arr, n));
}
}
 
// This code is contributed
// by Kirti_Mangal

Python 3




# Python 3 program to make all strings
# same using move to end operations.
import sys
 
# Returns minimum number of moves to end
# operations to make all strings same.
def minimunMoves(arr, n):
 
    ans = sys.maxsize
    for i in range(n):
 
        curr_count = 0
 
        # Consider s[i] as target string and
        # count rotations required to make
        # all other strings same as str[i].
        for j in range(n):
 
            tmp = arr[j] + arr[j]
 
            # find function returns the index where
            # we found arr[i] which is actually
            # count of move-to-front operations.
            index = tmp.find(arr[i])
 
            # If any two strings are not rotations of
            # each other, we can't make them same.
            if (index == len(arr[i])):
                return -1
 
            curr_count += index
 
        ans = min(curr_count, ans)
 
    return ans
 
# Driver Code
if __name__ == "__main__":
     
    arr = ["xzzwo", "zwoxz", "zzwox", "xzzwo"]
    n = len(arr)
    print( minimunMoves(arr, n))
 
# This code is contributed by ita_c

C#




using System;
 
// C# program to make all
// strings same using move
// to end operations.
public class GFG
{
 
// Returns minimum number of
// moves to end operations
// to make all strings same.
public  static int minimunMoves(string[] arr, int n)
{
    int ans = int.MaxValue;
    for (int i = 0; i < n; i++)
    {
        int curr_count = 0;
 
        // Consider s[i] as target
        // string and count rotations
        // required to make all other
        // strings same as str[i].
        string tmp = "";
        for (int j = 0; j < n; j++)
        {
            tmp = arr[j] + arr[j];
 
            // find function returns the
            // index where we found arr[i]
            // which is actually count of
            // move-to-front operations.
            int index = tmp.IndexOf(arr[i], StringComparison.Ordinal);
 
            // If any two strings are not
            // rotations of each other,
            // we can't make them same.
            if (index == arr[i].Length)
            {
                return -1;
            }
 
            curr_count += index;
        }
 
        ans = Math.Min(curr_count, ans);
    }
 
    return ans;
}
 
// Driver code
public static void Main(string[] args)
{
    string[] arr = new string[] {"xzzwo", "zwoxz", "zzwox", "xzzwo"};
    int n = arr.Length;
    Console.WriteLine(minimunMoves(arr, n));
}
}
 
// This code is contributed by Shrikant13

Javascript




<script>
 
// Javascript program to make all
// strings same using move
// to end operations.
     
    // Returns minimum number of
    // moves to end operations
    // to make all strings same.
    function minimunMoves(arr,n)
    {
        let ans = Number.MAX_VALUE;
    for (let i = 0; i < n; i++)
    {
        let curr_count = 0;
   
        // Consider s[i] as target
        // string and count rotations
        // required to make all other
        // strings same as str[i].
        let tmp = "";
        for (let j = 0; j < n; j++)
        {
            tmp = arr[j] + arr[j];
   
            // find function returns the
            // index where we found arr[i]
            // which is actually count of
            // move-to-front operations.
            let index = tmp.indexOf(arr[i]);
   
            // If any two strings are not
            // rotations of each other,
            // we can't make them same.
            if (index == arr[i].length)
                return -1;
                   
            curr_count += index;
        }
   
        ans = Math.min(curr_count, ans);
    }
   
    return ans;
    }
     
    // Driver code
    let arr=["xzzwo", "zwoxz",
                    "zzwox", "xzzwo"];
    let n = arr.length;
    document.write(minimunMoves(arr, n));
    
     
    // This code is contributed by avanitrachhadiya2155
     
</script>

Output:  

5

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