UVA 12627 - Erratic Expansion

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cstring>
using namespace std;
const int INF = 0x7fffffff;
int T;

long long my_pow(long long a, long long n)
{
long long res = 1;
for(int i = 0; i < n; ++i) res *= a;
return res;
}

long long dfs(long long k, long long c)
{
if(c == 0) return 0LL;
if(k == 0) return 1LL;
if(c >= my_pow(2, k-1)) return 2 * dfs(k-1, c - my_pow(2, k-1)) + my_pow(3, k - 1);
else return dfs(k-1, c);
}

int main()
{
scanf("%d", &T);
int CASE = 0;
while(T--) {
long long k, a, b;
scanf("%lld%lld%lld", &k, &a, &b);
printf("Case %d: %lld\n", ++CASE, dfs(k, (1 << k) - a + 1) - dfs(k, (1 << k) - b));
}
return 0;
}