This tutorial provides Java and Python solution to "Save the Prisoner!" problem of Hackerrank.

Hackerrank Challenge Details

Problem Statement:

A jail has N prisoners, and each prisoner has a unique id number, S, ranging from 1 to N. There are M sweets that must be distributed to the prisoners.

The jailer decides the fairest way to do this is by sitting the prisoners down in a circle (ordered by ascending S), and then, starting with some random S, distribute one candy at a time to each sequentially numbered prisoner until all M candies are distributed. For example, if the jailer picks prisoner S = 2, then his distribution order would be (2, 3, 4, 5,..., n-1, n, 1, 2, 3, 4,...) until all M sweets are distributed.

But wait—there's a catch—the very last sweet is poisoned! Can you find and print the ID number of the last prisoner to receive a sweet so he can be warned?

Input Format:

The first line contains an integer, T, denoting the number of test cases. 
The T subsequent lines each contain 3 space-separated integers: 
  N (the number of prisoners), M (the number of sweets), and S (the prisoner ID), respectively.

Output Format:

For each test case, print the ID number of the prisoner who receives the poisoned sweet on a new line.

Sample Input:

1 
5 2 1

Sample Output:

2

Explanation:

There are N = 5 prisoners and M = 2 sweets. Distribution starts at ID number S = 1, so prisoner 1 gets the first sweet and prisoner 2 gets the second (last) sweet. Thus, we must warn prisoner 2 about the poison, so we print 2 on a new line.

Solution Details

Java Implementation:

package com.saintech.allprogtutorials.hackerrank.algos;

import java.util.Scanner;

/**
 * @author Sain Technology Solutions
 *
 * Solution to Problem - https://www.hackerrank.com/challenges/save-the-prisoner
 */
public class SavePrisoner {
	
	private static int getConcernedPrisoner(int N, int M, int S) {
		final int prisonerId = (S + (M - 1)) % N;
		//if prisonerId comes as 0 means we are talking about Nth as Mod will never give us N
		return prisonerId == 0 ? N : prisonerId;
	}
	
	public static void main(String[] args) {
		final Scanner in = new Scanner(System.in);
		final int T = Integer.parseInt(in.next());
		for(int i = 0; i < T; i++) {
			final int N = Integer.parseInt(in.next());
			final int M =  Integer.parseInt(in.next());
			final int S = Integer.parseInt(in.next());
			System.out.println(getConcernedPrisoner(N, M, S));
		}
		in.close();
	}
}

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