总流程是递归：参考

方法一：用visited记录是否遍历

class Solution {public:    vector
     
      
        > permute(vector
       
         &num) {        vector
        
         
           > res;        vector
          
            out; vector
           
             visited(num.size(), 0); permuteDFS(num, 0, visited, out, res); return res; } void permuteDFS(vector
            
              &num, int level, vector
             
               &visited, vector
              
                &out, vector
               
                
                  > &res) { if (level == num.size()) res.push_back(out); else { for (int i = 0; i < num.size(); ++i) { if (visited[i] == 0) { visited[i] = 1; out.push_back(num[i]); permuteDFS(num, level + 1, visited, out, res); out.pop_back(); visited[i] = 0; } } } }};
                
               
              
             
            
           
          
         
        
       
      
     

 

方法二：交换数字

class Solution {public:    vector
     
      
        > permute(vector
       
         &num) {        vector
        
         
           > res;        permuteDFS(num, 0, res);        return res;    }    void permuteDFS(vector
          
            &num, int start, vector
           
            
              > &res) { if (start >= num.size()) res.push_back(num); for (int i = start; i < num.size(); ++i) { swap(num[start], num[i]); permuteDFS(num, start + 1, res); swap(num[start], num[i]); } }};