getting TLE for subtask-1 and got AC for subtask-2 &3

for the DIVSUBS problem(DIVSUBS) i am getting TLE for subtask-1 (range of input is 1<=n<=15), but for subtask-2 (range of input is 1<=n<=1000) and subtask-3 (range of input is 1<=n<=10^5) i got AC. how can this happen ?? By solution can be viewed here, what is the bug in my code??