OJ Board

Getting TLE :(
#include <iostream>
#include <vector>
#include <math.h>
#include <cstring>
using namespace std;
#define MAX 1048576
vector<int> primes;

void markMultiples(bool arr[], int a, int n)
{
int i = 2, num;
while ((num = i*a) <= n)
{
arr[num - 1] = 1; // minus 1 because index starts ...