terminusdeus / data-to-tree-task

data-to-tree-task

data-to-tree-task's Issues

Solution review

Hi, i'm the one who was running the interview; thanks for sending the complete solution, there might have been some pressure during the call - both as it requires coding on a sort of "white board" in the limited time period, and the fact we had to use English - it's really no-go here w/o the language knowledge, the client team members speak fast west coast American English, and some of asian origin have different accents + it's de-facto the only way to communicate here locally till one gets familiar with intermediate level Polish.

There are still few problems with this solution:

1. A minor one - you sort IDs to pass the smallest one, generally you only need the one where parent_id is zero + sorting to find the minimal element is overkill (N*logN vs. just N to scan)
2. If you pass some sort of data where a child comes before the parent in the list - which is totally possible if the in-database tree is being edited - you'll find out it doesn't work; try

var input = []Data{
	{1, 0, "str1"},
	{2, 4, "str2"},
	{3, 4, "str3"},
	{4, 1, "str4"},
	{5, 1, "str5"}}

3. The code complexity is at least O(N**2); a faster O(N) solution, which is also must easier to implement is to create a map[int]*InMemory - indexed by ID with empty children - and then scan this map again adding each scanned element to thatMap[element.ParentID].Children, finally finding the one with ParentID == 0 and returning it.
4. An extra question is usually - is it possible to create some loop in such an in-database tree and how to make the code detect such sort of loop.