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].

 

 

class Solution {public:    vector
    
     
       > permute(vector
      
        &num) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        vector
       
        
          > rel;        int level = 0;                permuteRec( rel, num, level);                return rel;    }    private:      void permuteRec( vector
         
          
            > & rel, vector
           
             &num, int level) { if( level == num.size() ) { rel.push_back( num ); return; } for( int i=level; i