Time complexity analysis of algorithm

Question

Hi I\'m trying to analyze the time complexity of this algorithm but I\'m having difficult unraveling and counting how many times the final loop will execute. I realize that the

Answer 1

It is O(n).

1 + 2 + 4 + ... + 2^N == 2^(N + 1) - 1.

The last loop, for a specific j, executes j times.

And for a specific i, the inner 2 loops execute 1 + 2 + 4 + ... + i times, which is equal to about 2 * i.

So the total execution times is 1 * 2 + 2 * 2 + 4 * 2 + ... + N * 2, which is about 4 * N.