Tricky Google interview question

Question

A friend of mine is interviewing for a job. One of the interview questions got me thinking, just wanted some feedback.

There are 2 non-negative integers: i and j. Gi

Answer 1

Use a Min-heap.

Put 1.

extract-Min. Say you get x.

Push 2x and 5x into the heap.

Repeat.

Instead of storing x = 2^i * 5^j, you can store (i,j) and use a custom compare function.