leetcode---Permutations

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], and [3,2,1].

方法1：

class Solution {
public:
vector<vector<int>> permute(vector<int>& nums)
{
vector<vector<int>> ans;
sort(nums.begin(), nums.end());
int n = nums.size();
do
{
vector<int> tmp;
for(int i=0; i<n; i++)
tmp.push_back(nums[i]);
ans.push_back(tmp);
}while(next_permutation(nums.begin(), nums.end()));
return ans;
}
};

方法2：

class Solution {
public:
vector<vector<int>> ans;
vector<int> tmp;

void dfs(int depth, vector<int>& nums)
{
if(depth >= nums.size()-1)
{
tmp.clear();
for(int i=0; i<nums.size(); i++)
tmp.push_back(nums[i]);
ans.push_back(tmp);
return;
}
for(int i=depth; i<nums.size(); i++)
{
swap(nums[depth], nums[i]);
dfs(depth+1, nums);
swap(nums[depth], nums[i]);
}
}

vector<vector<int>> permute(vector<int>& nums)
{
dfs(0, nums);
return ans;
}
};