Find winner of game where in each step a value from given Array is reduced from X

Last Updated : 01 Nov, 2022

You are given an arr[] of distinct positive integers along with an integer X (X ? 1). arr[] contains only 1 and all possible powers of prime number such that every element of arr[] is at most X. Two players A and B are playing a game on integer X alternatively. In each turn, one can choose a number arr[i] from arr[] such that arr[i]? X and update X to X - arr[i]. The game goes on until X becomes 0. The task is to find the winner if A starts first and both play optimally.

Examples:

Input: arr[] = {1, 2, 3, 4, 5, 7}, X = 7
Output: A
Explanation: Player A choose arr[5] = 7 from the arr[] and update X to 7 - 7 = 0.
Therefore, A wins the game because B can't make any move on 0.

Input: arr[] = {1}, X = 1
Output: A
Explanation: Player A choose arr[0] = 1 from the arr[] and update X to 1 - 1 = 0.
Therefore, A wins the game because B can't make any move on 0.

Approach: Implement the idea below to solve the problem

if X % 6 = 0. Then, player B wins else player A wins.

Proof of the approach:

Let's see the cases for X = [1, 2, 3, . . . ., 7]

For X = 1: arr[] will be: {1}

Player A can subtract 1 from X .So, that X becomes 0 and player B can't make any move on X further.Therefore, player A wins.

For X = 2: arr[] will be: {1, 2}

Player A can subtract 2 from X .So, that X becomes 0 and player B can't make any move on X further.Therefore, player A wins.

For X = 3: arr[] will be: {1, 2, 3}

Player A can subtract 3 from X .So, that X becomes 0 and player B can't make any move on X further.Therefore, player A wins.

For X = 4: arr[] will be: {1, 2, 3, 4}

Player A can subtract 4 from X .So, that X becomes 0 and player B can't make any move on X further.Therefore, player A wins.

For X = 5: arr[] will be: {1, 2, 3, 4, 5}

Player A can subtract 5 from X .So, that X becomes 0 and player B can't make any move on X further.Therefore, player A wins.

For X = 6: arr[] will be: {1, 2, 3, 4, 5}

Player A loses here.

All possible cases:

(i) Player A makes X as = (6-1) = 5, Player B can directly subtract 5.Hence B wins.
(ii) Player A makes X as = (6-2) = 4, Player B can directly subtract 4.Hence B wins.
(iii) Player A makes X as = (6-3) = 3, Player B can directly subtract 3.Hence B wins.
(iv) Player A makes X as = (6-4) = 2, Player B can directly subtract 2.Hence B wins.
(v) Player A makes X as = (6-5) = 1, Player B can directly subtract 1.Hence B wins.

In all above cases it can be verified that there is no such move possible so that A can be winner of the game.

For X = 7: arr[] will be: {1, 2, 3, 4, 5, 7}

Player A can subtract 7 from X .So, that X becomes 0 and player B can't make any move on X further.Therefore, player A wins.
Till, Now We observe a pattern that if X is a multiple of 6, Then B wins else A wins.

Below is the implementation of the above approach.

C++

#include <bits/stdc++.h>
using namespace std;

// Function which is called in main()
string Find_Winner(int X)
{

  // Checking if X is a multiple of 6
  if (X % 6 == 0) {
    return "B";
  }

  // If X is not a multiple of 6
  else {
    return "A";
  }
}

int main()
{

  int X = 7;
  int arr[] = { 1, 2, 3, 4, 5, 7 };

  // Function call
  cout << Find_Winner(X);
  return 0;
}

// This code is contributed by akashish__

Java

// Java code to implement the approach:

import java.io.*;

class GFG {

    // Driver Function
    public static void main(String[] args)
    {
        int X = 7;
        int[] arr = { 1, 2, 3, 4, 5, 7 };

        // Function call
        System.out.println(Find_Winner(X));
    }

    // Function which is called in main()
    static String Find_Winner(int X)
    {

        // Checking if X is a multiple of 6
        if (X % 6 == 0) {
            return "B";
        }

        // If X is not a multiple of 6
        else {
            return "A";
        }
    }
}

Python3

# python3 code to implement the approach:

# Function which is called in main()
def Find_Winner(X):

    # Checking if X is a multiple of 6
    if (X % 6 == 0):
        return "B"

    # If X is not a multiple of 6
    else:
        return "A"

# Driver Function
if __name__ == "__main__":

    X = 7
    arr = [1, 2, 3, 4, 5, 7]

    # Function call
    print(Find_Winner(X))

    # This code is contributed by rakeshsahni

// C# code to implement the above approach:
using System;
public class GFG {

  // Driver Function
  public static void Main(string[] args)
  {
    int X = 7;
    int[] arr = { 1, 2, 3, 4, 5, 7 };

    // Function call
    Console.WriteLine(Find_Winner(X));
  }

  // Function which is called in main()
  static string Find_Winner(int X)
  {

    // Checking if X is a multiple of 6
    if (X % 6 == 0) {
      return "B";
    }

    // If X is not a multiple of 6
    else {
      return "A";
    }
  }
}

// This code is contributed by AnkThon

JavaScript

// Javascript code to implement the approach:

// Driver Function

let X = 7;
let arr = [1, 2, 3, 4, 5, 7]

// Function call
console.log(Find_Winner(X));


// Function which is called in main()
function Find_Winner(X) {

    // Checking if X is a multiple of 6
    if (X % 6 == 0) {
        return "B";
    }

    // If X is not a multiple of 6
    else {
        return "A";
    }
}

// This code is contributed saurabh_jaiswal.