Permutations II Python Solution with Tests

Tested Python solution for LeetCode 47 with 12 pytest cases. Generate a practice environment with lcpy.

LeetCode 47, Medium. Topics: Array, Backtracking, Sorting. View on LeetCode.

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

lcpy gen -n 47   # by problem number
lcpy gen -s permutations_ii   # by problem name

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Problem

Given a collection of numbers, nums, that might contain duplicates, return all possible unique permutations in any order.

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Examples

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

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

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Constraints

• 1 <= nums.length <= 8
• -10 <= nums[i] <= 10

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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)
    def permute_unique(self, nums: list[int]) -> list[list[int]]:
        nums.sort()
        result: list[list[int]] = []
        used = [False] * len(nums)

        def backtrack(current: list[int]) -> None:
            if len(current) == len(nums):
                result.append(list(current))
                return
            for i in range(len(nums)):
                if used[i]:
                    continue
                if i > 0 and nums[i] == nums[i - 1] and not used[i - 1]:
                    continue
                used[i] = True
                current.append(nums[i])
                backtrack(current)
                current.pop()
                used[i] = False

        backtrack([])
        return result

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Complexity

Time	Space
O(n * n!)	O(n)

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Tags

NeetCode 250, NeetCode All.