[leetcode-47-Permutations II]

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],
[2,1,1]
]

思路：

    void permuteUniqueCore(vector<vector<int>>& result, vector<int>  nums, int index)
    {
        if (index == nums.size())
        {
            result.push_back(nums);
        }
        for (int i = index; i < nums.size(); i++)
        {
            if (i!=index && nums[i]==nums[index])continue;//
            swap(nums[i], nums[index]);
            permuteUniqueCore(result, nums, index + 1);
            //swap(nums[i], nums[index]);    //不要交换。。。了。。 参数nums 也是变成了传值 不是传引用        
        }
    }
    vector<vector<int>> permuteUnique(vector<int>& nums)
    {
        vector<vector<int>>result;        
        sort(nums.begin(), nums.end());         
        permuteUniqueCore(result, nums, 0);
        return result;
    }

参考：

http://www.cnblogs.com/crazyacking/p/5255205.html