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Minimum number of pigs required to find the poisonous bucket
  • Difficulty Level : Medium
  • Last Updated : 20 Apr, 2021

Given an integer N denoting the number of buckets, and an integer M, denoting the minimum time in minutes required by a pig to die after drinking poison, the task is to find the minimum number of pigs required to figure out which bucket is poisonous within P minutes, if there is exactly one bucket with poison, while the rest is filled with water.

Examples:

Input: N = 1000, M = 15, P = 60
Output: 5
Explanation: Minimum number of pigs required to find the poisonous bucket is 5.

Input: N = 4, M = 15, P = 15
Output: 2
Explanation: Minimum number of pigs required to find the poisonous bucket is 2.

Approach: The given problem can be solved using the given observations:



  • A pig can be allowed to drink simultaneously on as many buckets as one would like, and the feeding takes no time.
  • After a pig has instantly finished drinking buckets, there has to be a cool downtime of M minutes. During this time, only observation is allowed and no feedings at all.
  • Any given bucket can be sampled an infinite number of times (by an unlimited number of pigs).

Now, P minutes to test and M minutes to die simply tells how many rounds the pigs can be used, i.e., how many times a pig can eat. Therefore, declare a variable called r = P(Minutes To Test) / M(Minutes To Die).

Consider the cases to understand the approach:

Case 1: If r = 1, i.e., the number of rounds is 1.
Example: 4 buckets, 15 minutes to die, and 15 minutes to test. The answer is 2. Suppose A and B represent 2 pigs, then the cases are:

Obviously, using the binary form to represent the solution as:

Conclusion: If there are x pigs, they can represent (encode) 2x buckets.

Case 2: If r > 1, i.e. the number of rounds is more than 1. Let below be the following notations:

  • 0 means the pig does not drink and die.
  • 1 means the pig drinks in the first (and only) round.

Generalizing the above results(t means the pig drinks in the t round and die): If there are t attempts, a (t + 1)-based number is used to represent (encode) the buckets. (That’s also why the first conclusion uses the 2-based number)

Example: 8 buckets, 15 buckets to die, and 40 buckets to test. Now, there are 2 (= (40/15).floor) attempts, as a result, 3-based number is used to encode the buckets. The minimum number of pigs required are 2 (= Math.log(8, 3).ceil).

Below is the implementation of the above approach:

C++




// C++ program for the above approach
 
#include <bits/stdc++.h>
using namespace std;
 
// Function to find the minimum number of pigs
// required to find the poisonous bucket
void poorPigs(int buckets,
              int minutesToDie,
              int minutesToTest)
{
    // Print the result
    cout << ceil(log(buckets)
                 / log((minutesToTest
                        / minutesToDie)
                       + 1));
}
 
// Driver Code
int main()
{
    int N = 1000, M = 15, P = 60;
    poorPigs(N, M, P);
 
    return 0;
}

Java




// Java program for the above approach
import java.io.*;
 
class GFG
{
 
  // Function to find the minimum number of pigs
  // required to find the poisonous bucket
  static void poorPigs(int buckets, int minutesToDie,
                       int minutesToTest)
  {
 
    // Print the result
    System.out.print((int)Math.ceil(
      Math.log(buckets)
      / Math.log((minutesToTest / minutesToDie)
                 + 1)));
  }
 
  // Driver Code
  public static void main(String[] args)
  {
    int N = 1000, M = 15, P = 60;
    poorPigs(N, M, P);
  }
}
 
// This code is contributed by Dharanendra L V.

Python3




# Python program for the above approach
import  math
 
# Function to find the minimum number of pigs
# required to find the poisonous bucket
def poorPigs(buckets, minutesToDie, minutesToTest):
   
    # Prthe result
    print(math.ceil(math.log(buckets)\
                    // math.log((minutesToTest \
                                 // minutesToDie) + 1)));
 
# Driver Code
if __name__ == '__main__':
    N = 1000;
    M = 15;
    P = 60;
    poorPigs(N, M, P);
 
# This code is contributed by 29AjayKumar

C#




// C# program for the above approach
using System;
class GFG
{
 
  // Function to find the minimum number of pigs
  // required to find the poisonous bucket
  static void poorPigs(int buckets, int minutesToDie,
                       int minutesToTest)
  {
 
    // Print the result
    Console.WriteLine((int)Math.Ceiling(
      Math.Log(buckets)
      / Math.Log((minutesToTest / minutesToDie)
                 + 1)));
  }
 
  // Driver Code
  static public void Main()
  {
    int N = 1000, M = 15, P = 60;
    poorPigs(N, M, P);
  }
}
 
// This code is contributed by jana_sayantan.

Javascript




<script>
// Javascript program for the above approach
 
  // Function to find the minimum number of pigs
  // required to find the poisonous bucket
  function poorPigs(buckets, minutesToDie,
                       minutesToTest)
  {
  
    // Print the result
    document.write(Math.ceil(
      Math.log(buckets)
      / Math.log((minutesToTest / minutesToDie)
                 + 1)));
  }
 
    // Driver Code
    let N = 1000, M = 15, P = 60;
    poorPigs(N, M, P);
 
// This code is contributed by souravghosh0416.
</script>
Output: 
5

 

Time Complexity: O(1)
Auxiliary Space: O(1)

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