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Minimize swaps required to maximize the count of elements replacing a greater element in an Array
  • Last Updated : 11 Oct, 2020
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Given an array A[], consisting of N elements, the task is to find the minimum number of swaps required such that array elements swapped to replace a higher element, in the original array, is maximized.

Examples:

Input: A[] = {4, 3, 3, 2, 5} 
Output:
Explanation: 
Swap 1: {4, 3, 3, 2, 5} -> {5, 3, 3, 2, 4
Swap 2: {5, 3, 3, 2, 4} -> {3, 3, 5, 2, 4} 
Swap 3: {3, 3, 5, 2, 4} -> {3, 3, 2, 5, 4} 
Therefore, elements {4, 3, 2} occupies original position of a higher element after swapping
Input:. A[] = {6, 5, 4, 3, 2, 1} 
OutputL 5

Naive Approach: The simplest approach to solve the problem can be implemented as follows:

  • Sort the array in ascending order.
  • Initialize two variables, result, and index, to store the count and the index up to which it has been considered in the original array, respectively.
  • Iterate over the array elements. For any element A[i], go to a value in the array which is greater than ai and increment the index variable accordingly.
  • After finding an element greater than A[i], increment result, and index.
  • If index has reached the end of the array, no elements are left to be swapped with previously checked elements.
  • Therefore, print count.

Below is the implementation of the above approach:
 



C++




// C++ Program to implement
// the above approach
#include <bits/stdc++.h>
using namespace std;
 
// Function to find the minimum
// number of swaps required
int countSwaps(int A[], int n)
{
    // Sort the array in ascending order
    sort(A, A + n);
 
    int ind = 1, res = 0;
 
    for (int i = 0; i < n; i++) {
 
        // Iterate until a greater element
        // is found
        while (ind < n and A[ind] == A[i])
 
            // Keep incrementing ind
            ind++;
 
        // If a greater element is found
        if (ind < n and A[ind] > A[i]) {
 
            // Increase count of swap
            res++;
 
            // Increment ind
            ind++;
        }
 
        // If end of array is reached
        if (ind >= n)
            break;
    }
 
    // Return the answer
    return res;
}
 
// Driver Code
int main()
{
 
    int A[] = { 4, 3, 3, 2, 5 };
    cout << countSwaps(A, 5);
 
    return 0;
}

Java




// Java Program to implement
// the above approach
import java.util.*;
class GFG{
 
// Function to find the minimum
// number of swaps required
static int countSwaps(int A[], int n)
{
    // Sort the array in ascending order
    Arrays.sort(A);
    int ind = 1, res = 0;
 
    for (int i = 0; i < n; i++)
    {
 
        // Iterate until a greater element
        // is found
        while (ind < n && A[ind] == A[i])
 
            // Keep incrementing ind
            ind++;
 
        // If a greater element is found
        if (ind < n && A[ind] > A[i])
        {
 
            // Increase count of swap
            res++;
 
            // Increment ind
            ind++;
        }
 
        // If end of array is reached
        if (ind >= n)
            break;
    }
 
    // Return the answer
    return res;
}
 
// Driver Code
public static void main(String[] args)
{
    int A[] = { 4, 3, 3, 2, 5 };
    System.out.print(countSwaps(A, 5));
}
}
 
// This code is contributed by gauravrajput1

Python3




# Python3 program to implement
# the above approach
 
# Function to find the minimum
# number of swaps required
def countSwaps(A, n):
 
    # Sort the array in ascending order
    A.sort()
 
    ind, res = 1, 0
 
    for i in range(n):
 
        # Iterate until a greater element
        # is found
        while (ind < n and A[ind] == A[i]):
 
            # Keep incrementing ind
            ind += 1
 
        # If a greater element is found
        if (ind < n and A[ind] > A[i]):
 
            # Increase count of swap
            res += 1
 
            # Increment ind
            ind += 1
 
        # If end of array is reached
        if (ind >= n):
            break
 
    # Return the answer
    return res
 
# Driver Code
A = [ 4, 3, 3, 2, 5 ]
 
print (countSwaps(A, 5))
 
# This code is contributed by chitranayal

C#




// C# Program to implement
// the above approach
using System;
class GFG{
 
// Function to find the minimum
// number of swaps required
static int countSwaps(int []A, int n)
{
    // Sort the array in ascending order
    Array.Sort(A);
    int ind = 1, res = 0;
 
    for (int i = 0; i < n; i++)
    {
 
        // Iterate until a greater element
        // is found
        while (ind < n && A[ind] == A[i])
 
            // Keep incrementing ind
            ind++;
 
        // If a greater element is found
        if (ind < n && A[ind] > A[i])
        {
 
            // Increase count of swap
            res++;
 
            // Increment ind
            ind++;
        }
 
        // If end of array is reached
        if (ind >= n)
            break;
    }
 
    // Return the answer
    return res;
}
 
// Driver Code
public static void Main(String[] args)
{
    int []A = { 4, 3, 3, 2, 5 };
    Console.Write(countSwaps(A, 5));
}
}
 
// This code is contributed by Amit Katiyar
Output: 
3

Time Complexity: O(N * log N) 
Auxiliary Space: O(1)
Efficient Approach: 
Since any swap between two unequal elements leads to an element replacing a higher element, it can be observed that the minimum number of swaps required is N – (the maximum frequency of an array element). Therefore, find the most frequent element in the array using HashMap, and print the result.
Below is the implementation of the above approach:
 

C++




// C++ Program to implement
// the above approach
#include <bits/stdc++.h>
using namespace std;
 
// Function to find the minimum
// number of swaps required
int countSwaps(int A[], int n)
{
    // Stores the frequency of the
    // array elements
    map<int, int> mp;
 
    // Stores maximum frequency
    int max_frequency = 0;
 
    // Find the max frequency
    for (int i = 0; i < n; i++) {
 
        // Update frequency
        mp[A[i]]++;
 
        // Update maximum frequency
        max_frequency
            = max(max_frequency, mp[A[i]]);
    }
 
    return n - max_frequency;
}
 
// Driver Code
int main()
{
 
    int A[] = { 6, 5, 4, 3, 2, 1 };
 
    // function call
    cout << countSwaps(A, 6);
 
    return 0;
}

Java




// Java Program to implement
// the above approach
import java.util.*;
class GFG{
 
// Function to find the minimum
// number of swaps required
static int countSwaps(int arr[], int n)
{
    // Stores the frequency of the
    // array elements
    HashMap<Integer,
              Integer> mp = new HashMap<Integer,
                                        Integer>();
 
    // Stores maximum frequency
    int max_frequency = 0;
 
    // Find the max frequency
    for (int i = 0; i < n; i++)
    {
 
        // Update frequency
        if(mp.containsKey(arr[i]))
        {
            mp.put(arr[i], mp.get(arr[i]) + 1);
        }
        else
        {
            mp.put(arr[i], 1);
        }
 
        // Update maximum frequency
        max_frequency = Math.max(max_frequency,
                                 mp.get(arr[i]));
    }
    return n - max_frequency;
}
 
// Driver Code
public static void main(String[] args)
{
    int A[] = { 6, 5, 4, 3, 2, 1 };
 
    // function call
    System.out.print(countSwaps(A, 6));
}
}
 
// This code is contributed by Rohit_ranjan

Python3




# Python3 Program to implement
# the above approach
 
# Function to find the minimum
# number of swaps required
def countSwaps(A, n):
     
    # Stores the frequency of the
    # array elements
    mp = {}
 
    # Stores maximum frequency
    max_frequency = 0
 
    # Find the max frequency
    for i in range(n):
 
        # Update frequency
        if A[i] in mp:
            mp[A[i]] += 1
        else:
            mp[A[i]] = 1
 
        # Update maximum frequency
        max_frequency = max(max_frequency,
                            mp[A[i]])
 
    return n - max_frequency
   
# Driver code
if __name__ == "__main__":   
 
      A = [6, 5, 4, 3, 2, 1]
     
    # function call
    print(countSwaps(A, 6))
 
# This code is contributed by divyeshrabadiya07

C#




// C# program to implement
// the above approach
using System;
using System.Collections.Generic;
 
class GFG{
 
// Function to find the minimum
// number of swaps required
static int countSwaps(int []arr, int n)
{
     
    // Stores the frequency of the
    // array elements
    Dictionary<int,
               int> mp = new Dictionary<int,
                                        int>();
 
    // Stores maximum frequency
    int max_frequency = 0;
 
    // Find the max frequency
    for(int i = 0; i < n; i++)
    {
         
        // Update frequency
        if(mp.ContainsKey(arr[i]))
        {
            mp[arr[i]] = mp[arr[i]] + 1;
        }
        else
        {
            mp.Add(arr[i], 1);
        }
 
        // Update maximum frequency
        max_frequency = Math.Max(max_frequency,
                                 mp[arr[i]]);
    }
    return n - max_frequency;
}
 
// Driver Code
public static void Main(String[] args)
{
    int []A = { 6, 5, 4, 3, 2, 1 };
 
    // Function call
    Console.Write(countSwaps(A, 6));
}
}
 
// This code is contributed by 29AjayKumar
Output: 
5

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

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