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==0||num.empty())
            return res;
        helper(num, 0,size, out, res);
        return res;
    }
    void helper(vector<int> &num,int start,int size,vector<int> &out,vector<vector<int>> &res)
    {
        if(start==size-1)
        {
            for(int i=0;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+1,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,0,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+1,res);
        }
    }
};