[leetcode] Permutations

Permutations

思路：交换+DFS

class Solution {    vector<vector<int> > res;    int length;    public:    vector<vector<int> > permute(vector<int> &num) {        length=num.size();//有length个数        res.clear();        perm(num,0);        return res;    }    void perm(vector<int> &num,int i){        if (i==length) {            res.push_back(num);        }        for (int j=i; j<length; j++) {            swap(num[i], num[j]);            perm(num, i+1);            swap(num[j], num[i]);        }            }};

Reference：

permutations的讨论