Solution: Smallest Number Range

The question states "Given ‘M’ sorted arrays", however, there is a test case that contradicts this statement.

Input: [[1, 2, 3], [4, 13, 6], [7, 2, 7]]
Expected: [3,7]

Even if we assume that we sort these arrays to form:

Input: [[1, 2, 3], [4, 6, 13], [2, 7, 7]]

Shouldn't the expected answer be:

Expected: [2,4]

Since '2' exists in array 0 and 3, and '4' exists in array 1?

The key insight/ intuition (non-obvious) is that- if you did a worked example first- you'd find that the heap always contains ONLY 1 element from each list/ row array. The heap NEVER contains 2 or more elements from the SAME list.

This is important because it means that the range calculated at every iteration is always guaranteed to be a range that has exactly 1 element from every single list!

I think the description lacks this key detail, as it's just asserted that the stated solution works but it's not immediately obvious that it should.