LeetCode No.90 Subsets II

Given a collection of integers that might contain duplicates, nums, return all possible subsets.

Note: The solution set must not contain duplicate subsets.

For example,

If nums = 

[1,2,2]

, a solution is:

[
[2],
[1],
[1,2,2],
[2,2],
[1,2],
[]
]

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题目链接：https://leetcode.com/problems/subsets-ii/

题目大意：求出nums的所有子集，不能包含重复子集。

思路：dfs，先对nums进行排序，参数多加一个记录index表示当前可以dfs的下标，为了除重。

参考代码：

class Solution {
public:
vector<vector<int>> subsetsWithDup(vector<int>& nums) {
vector < vector <int> > ans ;
vector <int> ret ;
sort ( nums.begin() , nums.end() ) ;
dfs ( nums , ret , 0 , ans ) ;
return ans ;
}
private :
void dfs ( vector <int>& nums , vector <int> ret , int index , vector < vector <int> >& ans )
{
ans.push_back ( ret ) ;
if ( index >= nums.size() )
return ;
for ( int i = index ; i < nums.size() ; i ++ )
{
vector <int> temp = ret ;
temp.push_back ( nums[i] ) ;
dfs ( nums , temp , i + 1 , ans ) ;
while ( i + 1 < nums.size() && nums[i+1] == nums[i] )//除重
i ++ ;
}
}
};