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].

使用递归解决

class Solution {public:    vector
     
       visit;    vector
      
        num;    vector
       
        
          > res;    void dfs(int index , vector
         
          & sub){        if(index == num.size()){            res.push_back(sub);            return;        }                for(int i = 0 ; i < num.size(); ++ i){            if(!visit[i]){                visit[i] = true;                sub[index] = num[i];                dfs(index+1, sub);                visit[i] = false;            }        }    }    vector
          
           
             > permute(vector
            
              &num) { this->num = num; visit.resize(num.size(),false); vector
             
               sub(num.size(),0); dfs(0,sub); return res; }};