#include 
     
      using namespace std;void swap(char *a, char *b) {         char tmp;         tmp = *a;         *a = *b;         *b = tmp; }  void perm(char list[], int beg, int end) {         if(beg > end)         {                  for(int i = 0; i <= end; i++)                         cout << list[i];        cout << endl;    }         else         {                 for(int i = beg; i <= end; i++)                 {                         swap(&list[i], &list[beg]);                         perm(list, beg + 1, end);                         swap(&list[i], &list[beg]);                 }         } } int main() {         char list[] = {
   '1', '2', '3'};         int lens = sizeof(list) / sizeof(*list);    perm(list, 0, lens-1);         return 0; }
     

#include 
     
      #include 
      
       using namespace std;void getPer(vector
       
         &num, int index,         vector
        
          &tmp, vector
         
          
            > &rev){ if (index == num.size()) rev.push_back(tmp); for (int i = index; i < num.size(); ++i) { swap(num[i], num[index]); tmp.push_back(num[index]); getPer(num, index+1, tmp, rev); tmp.pop_back(); swap(num[i], num[index]); }}vector
           
            
              > permute(vector
             
               &nums){ vector
              
               
                 > rev; vector
                
                  tmp; getPer(nums, 0, tmp, rev); return rev;}int main(){ vector
                 
                   vec; vec.push_back(1); vec.push_back(2); vec.push_back(3); vector
                  
                   
                     > rev = permute(vec); cout << rev.size() << endl;}
                   
                  
                 
                
               
              
             
            
           
          
         
        
       
      
     

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