Minimum number of moves to make all elements equal

Given an array containing N elements and an integer K. It is allowed to perform the following operation any number of times on the given array:

Insert the K-th element at the end of the array and delete the first element of the array.

The task is to find the minimum number of moves needed to make all elements of the array equal. Print -1 if it is not possible.
Examples:

Input : arr[] = {1, 2, 3, 4}, K = 4
Output : 3
Step 1: 2 3 4 4
Step 2: 3 4 4 4
Step 3: 4 4 4 4

Input : arr[] = {2, 1}, K = 1
Output : -1
The array will keep alternating between 1, 2 and 
2, 1 regardless of how many moves you apply.

Let’s look at the operations with respect to the original array, first, we copy a[k] to the end, then a[k+1], and so on. To make sure that we only copy equal elements, all elements in the range K to N should be equal.
So, to find the minimum number of moves, we need to remove all elements in range 1 to K that are not equal to a[k]. Hence, we need to keep applying operations until we reach the rightmost term in range 1 to K that is not equal to a[k].
Below is the implementation of the above approach:

C++

// C++ Program to find minimum number of operations to make
// all array Elements equal
 
#include <bits/stdc++.h>

using namespace std;
 
// Function to find minimum number of operationsto make all
// array Elements equal

int countMinimumMoves(int arr[], int n, int k)
{

    int i;

    // Check if it is possible or not i.e., if all the

    // elements from index K to N are not equal

    for (i = k - 1; i < n; i++)

        if (arr[i] != arr[k - 1])

            return -1;

    // Find minimum number of moves

    for (i = k - 1; i >= 0; i--)

        if (arr[i] != arr[k - 1])

            return i + 1;

    // Elements are already equal

    return 0;
}
 
// Driver Code

int main()
{

    int arr[] = { 1, 2, 3, 4 };

    int K = 4;

    int n = sizeof(arr) / sizeof(arr[0]);

    cout << countMinimumMoves(arr, n, K);

    return 0;
}
 
// This code is contributed by Sania Kumari Gupta

// C Program to find minimum number of operations to make
// all array Elements equal
 
#include <stdio.h>
 
// Function to find minimum number of operations to make all
// array Elements equal

int countMinimumMoves(int arr[], int n, int k)
{

    int i;

    // Check if it is possible or not i.e., if all the

    // elements from index K to N are not equal

    for (i = k - 1; i < n; i++)

        if (arr[i] != arr[k - 1])

            return -1;

    // Find minimum number of moves

    for (i = k - 1; i >= 0; i--)

        if (arr[i] != arr[k - 1])

            return i + 1;

    // Elements are already equal

    return 0;
}
 
// Driver Code

int main()
{

    int arr[] = { 1, 2, 3, 4 };

    int K = 4;

    int n = sizeof(arr) / sizeof(arr[0]);

    printf("%d", countMinimumMoves(arr, n, K));

    return 0;
}
 
// This code is contributed by Sania Kumari Gupta

Java

// Java Program to find minimum number of operations to make
// all array Elements equal
 
import java.io.*;
 
class GFG {

    // Function to find minimum number of operations to make

    // all array Elements equal

    static int countMinimumMoves(int arr[], int n, int k)

    {

        int i;

        // Check if it is possible or not i.e., if all the

        // elements from index K to N are not equal

        for (i = k - 1; i < n; i++)

            if (arr[i] != arr[k - 1])

                return -1;

        // Find minimum number of moves

        for (i = k - 1; i >= 0; i--)

            if (arr[i] != arr[k - 1])

                return i + 1;

        // Elements are already equal

        return 0;

    }
 
    // Driver Code
 
    public static void main(String[] args)

    {

        int arr[] = { 1, 2, 3, 4 };

        int K = 4;

        int n = arr.length;

        System.out.print(countMinimumMoves(arr, n, K));

    }
}
 
// This code is contributed by Sania Kumari Gupta

Python3

# Python3 Program to find minimum 
# number of operations to make all 
# array Elements equal
 
# Function to find minimum number 
# of operations to make all array
# Elements equal

def countMinimumMoves(arr, n, k) :
 
    # Check if it is possible or not

    # That is if all the elements from

    # index K to N are not equal

    for i in range(k - 1, n) :

        if (arr[i] != arr[k - 1]) :

            return -1
 
    # Find minimum number of moves

    for i in range(k - 1, -1, -1) :

        if (arr[i] != arr[k - 1]) :

            return i + 1
 
    # Elements are already equal

    return 0
 
# Driver Code

if __name__ == "__main__" :
 
    arr = [ 1, 2, 3, 4 ]

    K = 4
 
    n = len(arr)
 
    print(countMinimumMoves(arr, n, K))
 
# This code is contributed by Ryuga

// C# Program to find minimum number of
// operations to make all array Elements
// equal

using System;
 
class GFG 
{

// Function to find minimum number 
// of operations to make all array
// Elements equal

static int countMinimumMoves(int []arr, 

                             int n, int k)
{

    int i;
 
    // Check if it is possible or not

    // That is if all the elements from

    // index K to N are not equal

    for (i = k - 1; i < n; i++)

        if (arr[i] != arr[k - 1])

            return -1;
 
    // Find minimum number of moves

    for (i = k - 1; i >= 0; i--)

        if (arr[i] != arr[k - 1])

            return i + 1;
 
    // Elements are already equal

    return 0;
}
 
// Driver Code

public static void Main ()
{

    int []arr = { 1, 2, 3, 4 };

    int K = 4;

    int n = arr.Length;

    Console.Write(countMinimumMoves(arr, n, K));
}
}
 
// This code is contributed 
// by 29AjayKumar

PHP

<?php
// PHP Program to find minimum number of
// operations to make all array Elements
// equal
 
// Function to find minimum number 
// of operations to make all array 
// Elements equal

function countMinimumMoves($arr, $n, $k)
{
 
    // Check if it is possible or not

    // That is if all the elements from

    // index K to N are not equal

    for ($i = $k - 1; $i < $n; $i++)

        if ($arr[$i] != $arr[$k - 1])

            return -1;
 
    // Find minimum number of moves

    for ($i = $k - 1; $i >= 0; $i--)

        if ($arr[$i] != $arr[$k - 1])

            return $i + 1;
 
    // Elements are already equal

    return 0;
}
 
// Driver Code

$arr = array(1, 2, 3, 4);

$K = 4;
 
$n = sizeof($arr);
 
echo countMinimumMoves($arr, $n, $K);
 
// This code is contributed 
// by Akanksha Rai
?>

Javascript

<script>
 
// JavaScript Program to find minimum number of
// operations to make all array Elements
// equal
 
// Function to find minimum number of operations
// to make all array Elements equal

function countMinimumMoves(arr, n, k)
{

    let i;
 
    // Check if it is possible or not

    // That is if all the elements from

    // index K to N are not equal

    for (i = k - 1; i < n; i++)

        if (arr[i] != arr[k - 1])

            return -1;
 
    // Find minimum number of moves

    for (i = k - 1; i >= 0; i--)

        if (arr[i] != arr[k - 1])

            return i + 1;
 
    // Elements are already equal

    return 0;
}
 
// Driver Code

    let arr = [ 1, 2, 3, 4 ];

    let K = 4;
 
    let n = arr.length;
 
    document.write(countMinimumMoves(arr, n, K));
 
// This code is contributed by Surbhi Tyagi.
 
</script>

Output:

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

Article Tags :

Algorithms

Arrays

DSA

Constructive Algorithms