Minimum number of swaps required to sort an array

Posted 2021-01-06 lightwindy

https://www.hackerrank.com/challenges/minimum-swaps-2/problem

Minimum Swaps II

You are given an unordered array consisting of consecutive integers  [1, 2, 3, ..., n] without any duplicates. You are allowed to swap any two elements. You need to find the minimum number of swaps required to sort the array in ascending order.

For example, given the array  we perform the following steps:

i   arr                         swap (indices)
0   [7, 1, 3, 2, 4, 5, 6]   swap (0,3)
1   [2, 1, 3, 7, 4, 5, 6]   swap (0,1)
2   [1, 2, 3, 7, 4, 5, 6]   swap (3,4)
3   [1, 2, 3, 4, 7, 5, 6]   swap (4,5)
4   [1, 2, 3, 4, 5, 7, 6]   swap (5,6)
5   [1, 2, 3, 4, 5, 6, 7]

It took  swaps to sort the array.

Function Description

Complete the function minimumSwaps in the editor below. It must return an integer representing the minimum number of swaps to sort the array.

minimumSwaps has the following parameter(s):

• arr: an unordered array of integers

Input Format

The first line contains an integer, , the size of . 
The second line contains  space-separated integers .

Constraints

 

Output Format

Return the minimum number of swaps to sort the given array.

Sample Input 0

4
4 3 1 2

Sample Output 0

3

Explanation 0

Given array  
After swapping  we get  
After swapping  we get  
After swapping  we get  
So, we need a minimum of  swaps to sort the array in ascending order.

Sample Input 1

5
2 3 4 1 5

Sample Output 1

3

Explanation 1

Given array  
After swapping  we get  
After swapping  we get  
After swapping  we get  
So, we need a minimum of  swaps to sort the array in ascending order.

Sample Input 2

7
1 3 5 2 4 6 8

Sample Output 2

3

Explanation 2

Given array  
After swapping  we get  
After swapping  we get  
After swapping  we get  
So, we need a minimum of  swaps to sort the array in ascending order.

 

https://www.geeksforgeeks.org/minimum-number-swaps-required-sort-array/

Given an array of n distinct elements, find the minimum number of swaps required to sort the array.

Examples:

Input : {4, 3, 2, 1}
Output : 2
Explanation : Swap index 0 with 3 and 1 with 2 to
form the sorted array {1, 2, 3, 4}.

Input : {1, 5, 4, 3, 2}
Output : 2

 

// Java program to find  minimum number of swaps
// required to sort an array
import javafx.util.Pair;
import java.util.ArrayList;
import java.util.*;
 
class GfG
{
    // Function returns the minimum number of swaps
    // required to sort the array
    public static int minSwaps(int[] arr)
    {
        int n = arr.length;
 
        // Create two arrays and use as pairs where first
        // array is element and second array
        // is position of first element
        ArrayList <Pair <Integer, Integer> > arrpos =
                  new ArrayList <Pair <Integer, Integer> > ();
        for (int i = 0; i < n; i++)
             arrpos.add(new Pair <Integer, Integer> (arr[i], i));
 
        // Sort the array by array element values to
        // get right position of every element as the
        // elements of second array.
        arrpos.sort(new Comparator<Pair<Integer, Integer>>()
        {
            @Override
            public int compare(Pair<Integer, Integer> o1,
                               Pair<Integer, Integer> o2)
            {
                if (o1.getKey() > o2.getKey())
                    return -1;
 
                // We can change this to make it then look at the
                // words alphabetical order
                else if (o1.getKey().equals(o2.getKey()))
                    return 0;
 
                else
                    return 1;
            }
        });
 
        // To keep track of visited elements. Initialize
        // all elements as not visited or false.
        Boolean[] vis = new Boolean[n];
        Arrays.fill(vis, false);
 
        // Initialize result
        int ans = 0;
 
        // Traverse array elements
        for (int i = 0; i < n; i++)
        {
            // already swapped and corrected or
            // already present at correct pos
            if (vis[i] || arrpos.get(i).getValue() == i)
                continue;
 
            // find out the number of  node in
            // this cycle and add in ans
            int cycle_size = 0;
            int j = i;
            while (!vis[j])
            {
                vis[j] = true;
 
                // move to next node
                j = arrpos.get(j).getValue();
                cycle_size++;
            }
 
            // Update answer by adding current cycle.
            ans += (cycle_size - 1);
        }
 
        // Return result
        return ans;
    }
}
 
// Driver class
class MinSwaps
{
    // Driver program to test the above function
    public static void main(String[] args)
    {
        int []a = {1, 5, 4, 3, 2};
        GfG g = new GfG();
        System.out.println(g.minSwaps(a));
    }
}
// This code is contributed by Saksham Seth