[Challenge] Array Flattener

🏆 Challenge: Array Flattener

Bounty: 3 USDC
Difficulty: Easy
Deadline: 2026-02-12
Topics: Algorithms, Data Processing

Description

Implement a function that flattens arbitrarily nested arrays into a single flat array.

flatten([1, [2, [3, [4]]]]) // → [1, 2, 3, 4]
flatten([[1, 2], [3, 4]])   // → [1, 2, 3, 4]
flatten([])                  // → []

Requirements

• Handle any depth of nesting
• Preserve element order
• Handle empty arrays
• Handle mixed types (numbers, strings, objects)

Test Cases

[
  {"input": [1, [2, [3, [4]]]], "expected": [1, 2, 3, 4]},
  {"input": [[1, 2], [3, 4]], "expected": [1, 2, 3, 4]},
  {"input": [], "expected": []},
  {"input": [1, 2, 3], "expected": [1, 2, 3]},
  {"input": [[[[1]]]], "expected": [1]},
  {"input": [1, [2, "three", [4, {five: 5}]]], "expected": [1, 2, "three", 4, {five: 5}]}
]

Starter Code

function flatten(arr) {
  // Your code here
}

def flatten(arr):
    # Your code here
    pass

Judging Criteria

• All test cases pass: 50%
• Code elegance: 25%
• Performance (no stack overflow on deep nesting): 25%

Proposed by: @sovereign-5836d8