SPCANDY - Editorial

editorial
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1

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DIFFICULTY

CAKEWALK

PREREQUISITES

Simple Math

PROBLEM

You wish to equally distribute N candies among M people, using the following algorithm

nCandies = 0
candies-with-each-person = 0

while nCandies ≥ M
	++candies-with-each-person
	nCandies = nCandies - M

Print the values of candies-with-each-person and nCandies at the end of the algorithm.

EXPLANATION

The given algorithm is an ad-hoc simultation of the division operation.

At the end of the algorithm, it is clear that

candies-with-each-person =
	quotient of N divided by M

and

nCandies =
	remainder of N divided by M

CODING COMMENTARY

There were two common pitfalls. The hint to both of them lay discreetly within the Constraints section.

M could be equal to 0

A lot of submissions received

Runtime Error: Floating Point Exception

verdict because of this pitfall.

The exact error of course is the attempted division by 0. Handling it as a special case is one solution.

N,M could be equal to 8,589,934,591

This typically led to a Wrong Answer verdict. The range of integers handled by the 32-bit signed integer datatype is typically

[-2147483648 2147483647]

One had to use 64-bit integer datatype to solve this problem. This means

  • long long in C/C++ - as CodeChef uses the GNU C++ Compiler
  • long in Java

PSEUDO CODE

Given: N, M

if M == 0
	return {
		candies-with-each-person = 0,
		nCandies = N
	}
else
	return {
		candies-with-each-person = N / M,
		nCandies = N % M
	}

Here, we assume that

  • N and M are 64-bit integers
  • % is the modulo operation

SETTER’S SOLUTION

Can be found here.

TESTER’S SOLUTION

Can be found here.

6 Likes
2

Whats wrong with this ?
http://www.codechef.com/viewsolution/2523298

3

@ajit_a Why is it scanf("%lld%d",&K,&N); and not scanf("%lld%lld",&K,&N);

N also needs to be long long.

4

Problem statement, replacing K by M:

while she has more than M candies

Editorial:

while nCandies ≥ M

‘More than’ means >, not >=

Let’s assume the problem statement was wrong, and it should have said ‘more than’.

Problem statement:

Your job is to tell how many candies will each student and the teacher
receive after the splitting is performed.

Editorial:

Handling [M=0] as a special case is one solution.

If M=0, then the algorithm provided in both the problem statement and editorial never terminates; it is undefined what happens after an infinite loop, not a special case.

5

Actually, the M=0 case here was to be interpreted as a special case, since the teacher can’t divide the candies by any students, since there are 0 students. On this case, the teacher receives all N candies… I’m sad this problem failed on being as trivial as possible due to this sort of complications… About the usage of long long it was really intended :slight_smile:

6

hi codechef ,

my below code is not working but same code is one user post that is working

what problem, in my code

using System;

namespace SplittingCandies
{

class Program
{

static void Main(string[] args)
{

int t = int.Parse(Console.ReadLine());
   
 for (int i = 0; i < t; i++)
        {
        
string[] tc = Console.ReadLine().Split(' ');
        
if (ulong.Parse(tc[1]) == 0)
         
   Console.WriteLine(tc[0] + " " + tc[1]);

else

   Console.WriteLine((ulong.Parse(tc[0]) / ulong.Parse(tc[1])) + " " + (ulong.Parse(tc[0]) % ulong.Parse(tc[1])));
      }
     Console.ReadLine();
    }
}

}

below code working this is one of user code

using System;

namespace SplittingCandies
{

class Program
{

static void Main(string[] args)
{

int cases = int.Parse(Console.ReadLine());

for (int i = 0; i < cases; i++)
{

string[] input = Console.ReadLine().Split(’ ');

if(ulong.Parse(input[1]) == 0)

Console.WriteLine(input[1] + " " + input[0]);

else

Console.WriteLine((ulong.Parse(input[0]) / ulong.Parse(input[1])) + " " + (ulong.Parse(input[0]) % ulong.Parse(input[1])));
}

Console.ReadLine();
}
}
}

7

0 case was somehow hidden very well

2 Likes
8

note: just pay attention to k, whether if it is 0 or not

9

note: just pay attention to k, whether if it is 0 or not

10

Why do we need to subtract candies at each stage and find the modulus and quotient at each stage?
Can’t we do it directly and in one step? Divide N by K, the quotient gives the candies each student will receive and the remainder the candies left with the teacher

11

@workforce , u are write but we have to take care when k=0 or n =0

12

why unsigned long cannot be used or simply long … as they are also of 8 byte ??? why only long long ???

13

@eabby007 unsigned long int range is from 0 to 4,294,967,295 (4 bytes!) wheras long long int is from -2^63 to 2^63-1 (8 bytes)