curriculum/challenges/english/blocks/daily-coding-challenges-python/69738771fb5a7b8b24cca29d.md
Given an array that contains nested arrays, return a new array with all values flattened into a single, one-dimensional array. Retain the original order of the items in the arrays.
flatten([1, [2, 3], 4]) should return [1, 2, 3, 4].
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(flatten([1, [2, 3], 4]), [1, 2, 3, 4])`)
}})
flatten([5, [4, [3, 2]], 1]) should return [5, 4, 3, 2, 1].
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(flatten([5, [4, [3, 2]], 1]), [5, 4, 3, 2, 1])`)
}})
flatten(["A", [[[["B"]]]], "C"]) should return ["A", "B", "C"].
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(flatten(["A", [[[["B"]]]], "C"]), ["A", "B", "C"])`)
}})
flatten([["L", "M", "N"], ["O", ["P", "Q", ["R", ["S", ["T", "U"]]]]], "V", ["W", ["X", ["Y", ["Z"]]]]]) should return ["L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"].
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(flatten([["L", "M", "N"], ["O", ["P", "Q", ["R", ["S", ["T", "U"]]]]], "V", ["W", ["X", ["Y", ["Z"]]]]]), ["L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"])`)
}})
flatten([["red", ["blue", ["green", ["yellow", ["purple"]]]]], "orange", ["pink", ["brown"]]]) should return ["red","blue","green","yellow","purple","orange","pink","brown"].
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(flatten([["red", ["blue", ["green", ["yellow", ["purple"]]]]], "orange", ["pink", ["brown"]]]), ["red","blue","green","yellow","purple","orange","pink","brown"])`)
}})
def flatten(arr):
return arr
def flatten(arr):
result = []
for item in arr:
if isinstance(item, list):
result.extend(flatten(item))
else:
result.append(item)
return result