Day 316 #644

Good morning! Here's your coding interview problem for today.

This problem was asked by Snapchat.

You are given an array of length N, where each element i represents the number of ways we can produce i units of change. For example, [1, 0, 1, 1, 2] would indicate that there is only one way to make 0, 2, or 3 units, and two ways of making 4 units.

Given such an array, determine the denominations that must be in use. In the case above, for example, there must be coins with value 2, 3, and 4.