Merge pull request #48 from Diegoslourenco/master

add PrimeGame class

Author: SarthakKeshari

CodeChef/PrimeGame.java

@@ -0,0 +1,114 @@
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+
+/*
+
+    QUESTION:
+
+    Chef and Divyam are playing a game with the following rules:
+
+    First, an integer X! is written on a board.
+    Chef and Divyam alternate turns; Chef plays first.
+    In each move, the current player should choose a positive integer D which is divisible by up to Y distinct primes
+    and does not exceed the integer currently written on the board. Note that 1 is not a prime.
+    D is then subtracted from the integer on the board, i.e. if the integer written on the board before this move was A,
+    it is erased and replaced by A−D.
+    When one player writes 0 on the board, the game ends and this player wins.
+    Given X and Y, determine the winner of the game.
+ */
+
+public class PrimeGame {
+
+    private static final int NUMBER = 1000000;
+    private static final int[] array = new int[NUMBER + 1];
+    private static final BufferedReader  br = new BufferedReader(new InputStreamReader(System.in));
+
+    public static void main(String[] args) throws IOException {
+
+        int t;
+        int chefPlay;
+        int divyamPlay;
+
+        boolean[] primes = getPrimesBySieveOfEratosthenes(NUMBER);
+        setArrayWithPrimes(primes);
+
+        t = Integer.parseInt(br.readLine());
+
+        while (t-- >= 0) {
+
+            String line = br.readLine();
+            String[] strings = line.split(" ");
+
+            chefPlay = Integer.parseInt(strings[0]);
+            divyamPlay = Integer.parseInt(strings[1]);
+
+            checkWinner(chefPlay, divyamPlay);
+        }
+
+        br.close();
+    }
+
+
+    /*
+        Receives 2 plays and checks and prints the winner
+     */
+    private static void checkWinner(int chefPlay, int divyamPlay) {
+        if (array[chefPlay] <= divyamPlay) {
+            System.out.println("Chef");
+        }
+        else {
+            System.out.println("Divyam");
+        }
+    }
+
+    /*
+        Receives a integer number and defines an boolean array with all primes smaller than or equal to
+        the number using Sieve of Eratosthenes algorithm
+        link: https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
+     */
+    private static boolean[] getPrimesBySieveOfEratosthenes(int number) {
+
+        /*
+            Create a boolean array "prime[0..n]" and initialize
+            all entries it as true. Each prime[i] will
+            finally be false if i is Not a prime, else true.
+        */
+        boolean[] prime = new boolean[number + 1];
+
+        for (int i = 0; i <= number; i++) {
+            prime[i] = true;
+        }
+
+        for (int p = 2; p * p <= number; p++) {
+
+            // If prime[p] is not changed, then it is a prime
+            if (prime[p]) {
+                // Update all multiples of p
+                for (int i = p*p; i <= number; i += p) {
+                    prime[i] = false;
+                }
+            }
+        }
+
+        return prime;
+    }
+
+    /*
+        Sets the array according to the givens primes array
+     */
+    private static void setArrayWithPrimes(boolean[] primes) {
+
+        array[0] = 0;
+        array[1] = 0;
+
+        for (int i = 2; i <= NUMBER; i++) {
+            array[i] = array[i - 1];
+
+            if (primes[i]) {
+                array[i] = array[i] + 1;
+            }
+        }
+    }
+
+}