Given a collection of numbers, return all possible permutations. For example, [1,2,3] have the following permutations: [1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], and [3,2,1]. http://leetcode.com/onlinejudge#question_46

leetcode_permutations.cpp

class Solution {
public:
    vector<vector<int> > permute(vector<int> &num) {
        vector< vector<int> > ans;
        ans.push_back(num);
        vector<int> id(num.size());
        for (int i = 0; i < id.size(); ++i)
            id[i] = i;
        while (next_permutation(id.begin(), id.end())) {
            vector<int> tmp;
            for (int i = 0; i < id.size(); ++i)
                tmp.push_back(num[id[i]]);
            ans.push_back(tmp);
        }
        return ans;
    }
};