Permutations II.txt

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

For example,
[1,1,2] have the following unique permutations:
[1,1,2], [1,2,1], and [2,1,1].
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solution：

void permuteUnique_aux(int index, vector<int>&num, vector<int>&tmp, vector<vector<int> >&ret, vector<bool>&isVisited)
{
    if(index == num.size())
    {
        ret.push_back(tmp);
        return;
    }
    for(int i = 0; i < num.size(); ++i)
    {
        if(isVisited[i] || (i != 0 && num[i] == num[i - 1] && isVisited[i - 1]))continue;
        isVisited[i] = true;
        tmp.push_back(num[i]);
        permuteUnique_aux(index + 1, num, tmp, ret, isVisited);
        isVisited[i] = false;
        tmp.pop_back();
    }
}
 
vector<vector<int> > permuteUnique(vector<int> &num)
{
    vector<vector<int> > ret;
    if(num.size() == 0)
        return ret;
    sort(num.begin(), num.end());
    vector<bool> isVisited(num.size(), false);
    vector<int> tmp;
    permuteUnique_aux(0, num, tmp, ret, isVisited);
    return ret;
}