Number Line Jumps HackerRank solution in Java

Java solution for Number Line Jumps HackerRank problem

Problem Description :

You are choreographing a circus show with various animals. For one act, you are given two kangaroos on a number line ready to jump in the positive direction.

• The first kangaroo starts at location x1 and moves at a rate of v1 meters per jump. 
• The second kangaroo starts at location x2 and moves at a rate of v2 meters per jump. 

You have to figure out a way to get both kangaroos at the same location at the same time as part of the show. If it is possible, return YES, otherwise return NO.

Example :

• x1 = 2
  
• v1 = 1
  
• x2 = 1
  
• v2 = 2

After one jump, they are both at x = 3, (x1 + v1 = 2 + 1, x2 + v2 = 1 + 2), so the answer is YES.

See full description :

Number Line Jump Problem Description 

Solution 1

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;

class Result {

    public static String kangaroo (int x1, int v1, int x2, int v2) {
        
        boolean canMatch = (v2 < v1);
        if (canMatch) {
            if ((x1 - x2) % (v2 - v1) == 0) {
               return "YES";
            }
        }
        return "NO";
    }

}

public class Solution {
    public static void main(String[] args) throws IOException {
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));

        String[] firstMultipleInput = bufferedReader.readLine().replaceAll("\\s+$", "").split(" ");

        int x1 = Integer.parseInt(firstMultipleInput[0]);

        int v1 = Integer.parseInt(firstMultipleInput[1]);

        int x2 = Integer.parseInt(firstMultipleInput[2]);

        int v2 = Integer.parseInt(firstMultipleInput[3]);

        String result = Result.kangaroo(x1, v1, x2, v2);

        bufferedWriter.write(result);
        bufferedWriter.newLine();

        bufferedReader.close();
        bufferedWriter.close();
    }
}

Solution explanation :

• In description, 0 <= x1 < x2 <= 10000. means x1 is always less than x2. 
• So we are checking v2 is less than v1 or not. because if v2 is greater than v1 then kangaroo1 never will catch kangaroo2 means both can not catch at same location with same jump.
• If we want to know where any kangaroo is at any given time we can directly check using following formula.
• (x1 - x2) % (v2 - v1) == 0 
• Using above formula if we get 0 then, we can print YES. Means both kangaroos reached same location with same jump.

Output explanation :

Output 1 :

• x1 = 0, v1 = 3, x2 = 4, v2 = 2
• If condition | v2 < v1 | 2 < 3 becomes true
• (x1 - x2) % (v2 - v1) == 0
• 0 - 4 % 2 - 3 = -4 % -1 = 0 
• 0 == 0 return YES. 

Output 2 :

• x1 = 0, v1 = 2, x2 = 5, v2 =3
• return NO
  

Lets see another solution using while loop

Solution 2

public static String kangaroo(int x1, int v1, int x2, int v2) {

    if ((x1 < x2 && v1 < v2) || (v1 == v2 && x1 != x2)) {
        return "NO";
    } else {
        int first = x1+v1, second = x2+v2;
        while (first != second) {
            first = first + v1;
            second = second + v2;
            
            if (v1 > v2 && first > second) {
                return "NO";
            }
        }
       return "YES";
    }
}

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