Flatten Array

Instructions

Take a nested list and return a single flattened list with all values except nil/null.

The challenge is to take an arbitrarily-deep nested list-like structure and produce a flattened structure without any nil/null values.

For example:

input: [1,[2,3,null,4],[null],5]

output: [1,2,3,4,5]

"Null" in Tcl

Tcl does not have a null or nil value. In practice, the empty string is often used to indicate "no value". But that can be tricky in situations where an empty string is actually a valid value, for example in a list representing a row of CSV data.

For this exercise, treat the empty string as a null value that is to be discarded.

---

Source

Interview Question