[LeetCode] Problem 47 - Permutations II

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

Example

Input: [1,1,2]

Output:

1
2
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5
[
  [1,1,2],
  [1,2,1],
  [2,1,1]
]

Code

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public List<List<Integer>> permuteUnique(int[] nums) {
    List<List<Integer>> result = new ArrayList<>();

    Arrays.sort(nums);
    permuteUniqueHelper(result, new ArrayList<>(), new boolean[nums.length], nums);

    return result;
}

private void permuteUniqueHelper(List<List<Integer>> result, List<Integer> permute, boolean[] visit, int[] nums) {
    if (permute.size() == nums.length) {
        result.add(new ArrayList<>(permute));
        return;
    }

    for (int i = 0; i < nums.length; i++) {
        if (visit[i] || (i > 0 && nums[i] == nums[i - 1] && !visit[i - 1]))
            continue;

        permute.add(nums[i]);
        visit[i] = true;
        permuteUniqueHelper(result, permute, visit, nums);
        permute.remove(permute.size() - 1);
        visit[i] = false;
    }
}