Given a collection of numbers that might contain duplicates, return all possible unique permutations.
Input: [1,1,2]
Output:
[
[1,1,2],
[1,2,1],
[2,1,1]
]
void helper(vector<int>& nums, int level, vector<int>& cur, vector<vector<int> >& res, vector<int>& visited) {
if (level >= nums.size()) {
res.push_back(cur);
} else {
for (int i = 0; i < nums.size(); ++i) {
if (visited[i] == 1) continue;
if (i > 0 && nums[i] == nums[i - 1] && visited[i - 1] == 0) continue;
visited[i] = 1;
cur.push_back(nums[i]);
helper(nums, level + 1, cur, res, visited);
cur.pop_back();
visited[i] = 0;
}
}
}
vector<vector<int>> permuteUnique(vector<int>& nums) { // time: O(n!); space: O(n!)
sort(nums.begin(), nums.end());
vector<vector<int> > res;
vector<int> cur, visited(nums.size(), 0);
helper(nums, 0, cur, res, visited);
return res;
}