# 47. Permutations II

## 刷题内容

• https://leetcode.com/problems/permutations-ii/

Given a collection of numbers that might contain duplicates, return all possible unique permutations.

Example:

Input: [1,1,2]
Output:
[
[1,1,2],
[1,2,1],
[2,1,1]
]


˼·1 *- ʱ�临�Ӷ�: O(n!nlgn)*- �ռ临�Ӷ�: O(n)***

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class Solution {
public:
void DFS(int* visited,vector<int>& nums,set<vector<int> >& ans,vector<int> temp)
{
int count1 = 0;
for(int i = 0;i < nums.size();++i)
if(!visited[i])
{
temp.push_back(nums[i]);
visited[i] = 1;
DFS(visited,nums,ans,temp);
temp.pop_back();
visited[i] = 0;
count1 = 1;
}
if(!count1)
ans.insert(temp);
}
vector<vector<int>> permuteUnique(vector<int>& nums) {
vector<vector<int> > ans;
int visited[nums.size()];
memset(visited,0,sizeof(visited));
set<vector<int> > s;
vector<int> temp;
for(int i = 0; i < nums.size();++i)
{
visited[i] = 1;
temp.push_back(nums[i]);
DFS(visited,nums,s,temp);
temp.pop_back();
visited[i] = 0;
}
for(auto pos = s.begin();pos != s.end();++pos)
ans.push_back(*pos);
return ans;
}
};


˼·2 **- ʱ�临�Ӷ�: O(n!)*- �ռ临�Ӷ�: O(n)***

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class Solution {
public:
vector<vector<int>> permuteUnique(vector<int>& nums) {
const int n = nums.size();
sort(nums.begin(), nums.end());
vector<vector<int>> ret;
vector<int> visited(n, 0), arr;
dfs(nums, ret, arr, visited);
return ret;
}
void dfs(vector<int>& nums, vector<vector<int>>& ret, vector<int>& arr, vector<int>& visited) {
if (arr.size() == nums.size()) {
ret.push_back(arr);
return;
}
for (int i = 0; i < nums.size(); ++i) {
if (visited[i]) {continue;}
if (i -1 >= 0 && nums[i] == nums[i-1] && !visited[i-1]) {continue;}
arr.push_back(nums[i]);
visited[i] = 1;
dfs(nums, ret, arr, visited);
arr.pop_back();
visited[i] = 0;
}
}
};