Hacker Rank : Project Euler#1

Question

I am new to competitive programming and I did a problem on Hacker Rank. The question statement is as follows:

"If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below N.

Input Format First line contains T that denotes the number of test cases. This is followed by T lines, each containing an integer, N.

Output Format For each test case, print an integer that denotes the sum of all the multiples of 3 or 5 below N."

Constraints

1≤T≤10^5

1≤N≤10^9

I've written the following code which successfully satisfies 3 test cases and fails at remaining two.

#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>

int func(int p,int n)
{
    int j;
    n=n-1;
    j=n/p;
    return (p*j*(j+1))/2;
}

int main()
{
    unsigned long int n;
    int t,j,count;
    scanf("%d",&t);
  if(t>=1 && t<=100000){
        for(j=0;j<t;j++)
        {
            scanf("%lu",&n);
        if(n>=1 && n<=1000000000)
        {
                count=func(3,n)+func(5,n)-func(15,n);
                printf("%d\n",count);
            }

        }}
    return 0;
}

What is the mistake in my code. Why isn't it getting accepted?

Answer 1

There are a couple of issues.

You are indeed overflowing your int when returning from func. Also, your printf statement should be printf("%llu\n", count);

So, the return from func, count, and the local variable j, should all be unsigned long long and your print out should reflect that as well. You need to make j unsigned long long because of the arithmetic in the return statement for func(this is at least the case in VS 2013).