# 47. 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]
]
# Solution
Approach 1: DFS with hash table.
# Code (Python)
Approach 1:
# Code (C++)
Approach 1:
class Solution {
private:
vector<vector<int>> res;
void permuteUnique(vector<int>& nums, int head) {
if (head == nums.size())
{
res.push_back(nums);
return;
}
unordered_set<int> visited;
for (int i = head; i < nums.size(); ++i)
{
if (visited.find(nums[i]) != visited.end())
continue;
visited.insert(nums[i]);
if (i > head)
std::swap(nums[head], nums[i]);
permuteUnique(nums, head + 1);
if (i > head)
std::swap(nums[head], nums[i]); // need to swap back.
}
}
public:
vector<vector<int>> permuteUnique(vector<int>& nums) {
permuteUnique(nums, 0);
return res;
}
};