[leetcode] 46. Permutations

Given a collection of distinct 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],  [3,2,1]]

解法一：

dp的思想，挨个生长随机数组。

class Solution {public:    vector<vector<int>> permute(vector<int>& nums) {        vector<vector<int> > res;        vector<int> first(1,nums[0]);        res.push_back(first);                for(int i=1; i<nums.size(); i++){            vector<vector<int> > tmp;            tmp = permuteSub(res, nums[i]);            res.clear();             res = tmp;        }        return res;            }        vector<vector<int> > permuteSub(vector<vector<int>> pre, int num){        vector<vector<int> > res;        for(int i=0; i<pre.size(); i++){            int len = pre[i].size();            for(int j=0; j<=len;j++){                vector<int> tmp = pre[i];                tmp.insert(tmp.begin()+j, num);                res.push_back(tmp);            }        }        return res;            }};