LeetCode 046 Permutations 全排列

Given a collection of distinct 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],
  [3,2,1]
]

方法一：

 class Solution {
 public:
      vector<vector<int> > permute(vector<int> &num) {
         vector<vector<int> > res;
         vector<int> out;
         int size=num.size();
         if(size==||num.empty())
             return res;
         helper(num, ,size, out, res);
         return res;
     }
     void helper(vector<int> &num,int start,int size,vector<int> &out,vector<vector<int>> &res)
     {
         if(start==size-)
         {
             for(int i=;i<size;++i)
                 out.push_back(num[i]);
             res.push_back(out);
             out.clear();
         }
         else
         {
             for(int i=start;i<size;++i)
             {
                 swap(num,start,i);
                 helper(num,start+,size,out,res);
                 swap(num,start,i);
             }
         }
     }
     void swap(vector<int> &num,int i,int j)
     {
         int tmp=num[i];
         num[i]=num[j];
         num[j]=tmp;
     }
 };

方法二：

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