Problem Statement
Write a function that takes in an array of unique integers and then returns an array of all unordered permutations.
Sample Input
array = [1, 2, 3]
Sample Result
[
[1, 2, 3],
[1, 3, 2],
[2, 1, 3],
[2, 3, 1],
[3, 1, 2],
[3, 2, 1]
]
Code #1
def get_permutations(array):
permutations = []
helper(0, array, permutations)
return permutations
def helper(i, array, permutations):
if i == len(array) - 1:
permutations.append(list(array))
else:
for j in range(i, len(array)):
swap(array, i, j)
helper(i + 1, array, permutations)
swap(array, i, j)
def swap(array, i, j):
array[i], array[j] = array[j], array[i]
Notes
- Assumption: if the input array is empty, return empty array.
- Try thinking of permutations as a graph.
- TODO: try the iterative approach.
Credits
- Algoexpert for the problem statement.
- Jean-Louis Paulin for the cover image (https://unsplash.com/photos/lHwmE58fW4Y).
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