Permutations Python Solution with Tests

Tested Python solution for LeetCode 46 with 12 pytest cases. Generate a practice environment with lcpy.

LeetCode 46, Medium. Topics: Array, Backtracking. View on LeetCode.

Generate this problem as a practice environment: tested reference solution, 12 parametrized pytest cases, and a playground notebook:

lcpy gen -n 46   # by problem number
lcpy gen -s permutations   # by problem name

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Problem

Given an array nums of distinct integers, return all the possible permutations. You can return the answer in any order.

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Examples

Input: nums = [1,2,3]
Output: [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]

Input: nums = [0,1]
Output: [[0,1],[1,0]]

Input: nums = [1]
Output: [[1]]

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Constraints

• 1 <= nums.length <= 6
• -10 <= nums[i] <= 10
• All the integers of nums are unique.

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Solution

Reference implementation from solution.py on GitHub, full suite in test_solution.py:

class Solution:
    # Time: O(n! * n)
    # Space: O(n! * n) output + O(n) recursion
    def permute(self, nums: list[int]) -> list[list[int]]:
        result = []

        def backtrack(start: int) -> None:
            if start == len(nums):
                result.append(nums[:])
                return

            for i in range(start, len(nums)):
                nums[start], nums[i] = nums[i], nums[start]
                backtrack(start + 1)
                nums[start], nums[i] = nums[i], nums[start]

        backtrack(0)
        return result

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Complexity

Time	Space
O(n! * n)	O(n! * n) output + O(n) recursion

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Tags

Grind 75, Grind, NeetCode 150, NeetCode 250, NeetCode All, AlgoMaster 75.