Lily’s Homework in Algorithm | HackerRank Programming Solutions | HackerRank Problem Solving Solutions in Java [💯Correct]

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Introduction To Algorithm

The word Algorithm means “a process or set of rules to be followed in calculations or other problem-solving operations”. Therefore Algorithm refers to a set of rules/instructions that step-by-step define how a work is to be executed upon in order to get the expected results. 

Advantages of Algorithms:

• It is easy to understand.
• Algorithm is a step-wise representation of a solution to a given problem.
• In Algorithm the problem is broken down into smaller pieces or steps hence, it is easier for the programmer to convert it into an actual program.

Link for the Problem – Lily’s Homework – Hacker Rank Solution

Lily's Homework – Hacker Rank Solution

Problem:

Whenever George asks Lily to hang out, she’s busy doing homework. George wants to help her finish it faster, but he’s in over his head! Can you help George understand Lily’s homework so she can hang out with him?

Consider an array of  distinct integers, . George can swap any two elements of the array any number of times. An array is beautiful if the sum of  among  is minimal.

Given the array , determine and return the minimum number of swaps that should be performed in order to make the array beautiful.

Example

One minimal array is . To get there, George performed the following swaps:

    Swap      Result
          [7, 15, 12, 3]
    3 7   [3, 15, 12, 7]
    7 15  [3, 7, 12, 15]
   

It took  swaps to make the array beautiful. This is minimal among the choices of beautiful arrays possible.

Function Description

Complete the lilysHomework function in the editor below.

lilysHomework has the following parameter(s):

• int arr[n]: an integer array

Returns

• int: the minimum number of swaps required

Input Format

The first line contains a single integer, , the number of elements in . The second line contains  space-separated integers, .

Constraints

Sample Input

STDIN       Function
-----       --------
4           arr[]size n = 4
2 5 3 1     arr = [2, 5, 3, 1]

Sample Output

2

Explanation

Define  to be the beautiful reordering of . The sum of the absolute values of differences between its adjacent elements is minimal among all permutations and only two swaps ( with  and then  with ) were performed.

Lily's Homework – Hacker Rank Solution

import java.io.*;
import java.math.*;
import java.security.*;
import java.text.*;
import java.util.*;
import java.util.concurrent.*;
import java.util.function.*;
import java.util.regex.*;
import java.util.stream.*;
import static java.util.stream.Collectors.joining;
import static java.util.stream.Collectors.toList;
import java.util.stream.IntStream;

public class LilysHomework {

    private static final Scanner scn = new Scanner(System.in);

    private static void swap(long[] array, int index1, int index2) {
        long temp = array[index1];
        array[index1] = array[index2];
        array[index2] = temp;
    }

    private static int swaps(long[] unsortedValues) {
        int swaps = 0;

        Map<Long, Integer> locations = new HashMap<>();
        for (int i = 0; i < unsortedValues.length; i++) {
            locations.put(unsortedValues[i], i);
        }

        long [] sortedValue = unsortedValues.clone();
        Arrays.sort(sortedValue);

        for (int i = 0; i < sortedValue.length; i++) {
            if (sortedValue[i] != unsortedValues[i]) {
                swaps++;

                int swapIndex = locations.get(sortedValue[i]);
                locations.put(unsortedValues[i], swapIndex);

                swap(unsortedValues, i, swapIndex);
            }
        }

        return swaps;
    }

    public static void main(String[] args) {
        int numberOfElements = scn.nextInt();
        long[] values = new long[numberOfElements];
        for (int i = 0; i < numberOfElements; i++) {
            int value = scn.nextInt();
            values[i] = value;
        }
        // When all you have is a hammer, everything begins to look like a nail.
        long [] reverseValue = IntStream.rangeClosed(1, values.length).mapToLong(
                i -> values[values.length - i]).toArray();
        System.out.println(Math.min(swaps(values), swaps(reverseValue)));

    }
}