Flatten Array

Instructions

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

The challenge is to write a function that accepts an arbitrarily-deep nested list-like structure and returns a flattened structure without any nil/null values.

For example:

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

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

You can think of this data structure as a Rose Tree. You are given a data type 'a tree that represents this data structure.

Notes

• For this exercise Empty represents null
• The nested list is represented by List [...].
• The input example is represented by List [Elem 1, List [Elem 2, Elem 3, Empty, Elem 4], List [Empty], Elem 5]

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Source

Interview Question