SRM 537 500 Problem

537-500.cpp

int KingXNewCurrency::howMany(int A, int B, int X) {
    int d = __gcd(A, B);
    if (d % X == 0) return -1;
    
    set <int> s1;
    for (int k = 0; A - k * X >= 0; k++){
        int a = A - k * X;
        for (int i = 1; i <= a; i++){
            if (i == X) continue;
            if (a % i == 0) s1.insert(i);
        }
    }
    
    set <int> s2;
    for (int k = 0; B - k * X >= 0; k++){
        int b = B - k * X;
        for (int i = 1; i <= b; i++){
            if (i == X) continue;
            if (b % i == 0) s2.insert(i);
        }
    }
    
    // If X|A or X|B all of the numbers are divisors
    if (A % X == 0) return s2.size();
    if (B % X == 0) return s1.size();
    
   
    // Count divisors of A - k * X and B - k * X 
    set <int> :: iterator it1 = s1.begin();
    set <int> :: iterator it2 = s2.begin();
    int count = 0;
    while (it1 != s1.end() and it2 != s2.end()){
        if (*it1 < *it2) it1++;
        else if (*it2 < *it1) it2++;
        else {count++; it1++; it2++;}
    }
    
    return count;
}