46. Permutations (Recursion, DP)

標籤：

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].

思路：遍曆數組，對於該字母，它可選擇與它之後的字母交換或者是不交換=>帶回溯的遞迴

class Solution {public:    vector<vector<int> > permute(vector<int> &num) {        result.clear();          dfs(num,0);        return result;            }    void dfs(vector<int> num, int depth)    {        if(depth == num.size()-1)        {            result.push_back(num);            return;        }        dfs(num,depth+1);        int temp = num[depth];        for(int i = depth+1;i< num.size(); i++)        {            num[depth] = num[i];            num[i] = temp;            dfs(num,depth+1);            num[i] = num[depth];            num[depth] = temp;        }    }    private:    vector<vector<int> >  result;};

 

46. Permutations (Recursion, DP)