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].
void permute(vector<int> &num, int index, vector<vector<int>> &res)
{
if(index>=num.size()){res.push_back(num);return;}
set<int> swapnum;
swapnum.insert(num[index]);
for(int i = index; i < num.size(); i++)
{
if(index != i)
{
set<int&......
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