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1

I am using the sieve of sundaram to get an array of primes upto 4000 and then doing binary search on it to find the next greatest prime then the sum of X and Y and outputting the different between the prime and the sum. but it gives me wrong answer.
help?

link to my code

https://www.codechef.com/viewsolution/16379802

2

Your binary function is wrong:
correct one is here:

   int binary(int z) {
int r = primes.size() - 1;
int l = 0;
while(l < r) {	
	int mid = (l + r) / 2;
	if(primes[mid] <= z and primes[mid+1] > z) 
		return primes[mid  +1];

	if(primes[mid] > z && primes[mid-1] <= z)
		return primes[mid];
	else if(primes[mid] <= z) //  <=
		l = mid + 1;
	else
		r = mid - 1;
}

}

3

thanks it worked.!!