# Board Exam - Editorial

Problem link: CodeChef: Practical coding for everyone

Author and Editorialist: saloni_203

DIFFICULTY:
CAKEWALK

PREREQUISITES:
None

PROBLEM:
Sneha is giving her board exam of Science. And her question paper has two parts Part A and Part B, each containing “N” questions. If she has to choose “X” questions from part A and “Y” questions from part B.
Then how many ways can she choose the questions.

Each part should have at least 1 question.

QUICK EXPLANATION:
Key to success : Anyone with good knowledge of combination can do this question very, very easily.
Sneha has to generate the combination of [N, X] and [N, Y].

EXPLANATION:
There are N questions in part A out of which X questions can be chosen in C(N, X) ways. Similarly, Y questions can be chosen from part B containing N questions in C(N, Y) ways.
So. the total number of ways of selecting x questions from part A and y questions from part B is C(N, X) * C(N, Y).

SOLUTION:

Editorialist's Solution

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

int fact(int);

int main()
{
int T;
cin>>T;
while(T–)
{
int n,x,y;
cin>>n>>x>>y;
if(n>=1 && x>0 && x<n && y>0 && y<n)
{
long long int w = (fact(n)/(fact(n-x)*fact(x))) * (fact(n)/(fact(n-y)*fact(y)));
cout<<w<<endl;
}
}
}
int fact(int l)
{
int i,f=1;
for(i=1;i<=l;i++)
{
f=f * i;
}
return f;
}

2 Likes

I don’t think this is an entirely correct solution, this would start failing when fact(n) becomes greater than range of long long int.
So either use multiprecision ints or use a loop to select the questions.

Solution is not according to constants , because N can be 100.

They changed the testcase many times during contest. I even tried to consider the constraints but they said that they are correct.

If this editorial is considered to be correct then the test cases are weak and the max value of N would be around 20.