题目：

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].

思路：

与
http://blog.csdn.net/lanxu_yy/article/details/17525459的思路有一些细微的区别。每次取出一个不同的数，然后利用剩下的数形成子集。

代码：

class Solution {
public:
    vector<vector<int> > permuteUnique(vector<int> &num) {
        sort(num.begin(),num.end());
        return generatePermute(num);
    }
    
    vector<vector<int>> generatePermute(vector<int> num)
    {
        vector<vector<int>> results;
        if(num.size()==1)
        {
            vector<int> tmp;
            tmp.push_back(num[0]);
            results.push_back(tmp);
            return results;
        }
        else
        {
            int pre=INT_MIN;
            int cur=num[0];
            int i=0;
            do
            {
                cur = num[i];
                if(cur!=pre)
                {
                    num.erase(num.begin()+i);
                    vector<vector<int>> r = generatePermute(num);
                    for(int k=0;k<r.size();k++)
                    {
                        r[k].insert(r[k].begin(),cur);
                        results.push_back(r[k]);
                    }
                    num.insert(num.begin()+i,cur);
                }
                pre = cur;
                i++;
            }
            while(i<num.size());
            return results;
        }
    }
};