Leetcode 47. Permutations II (Medium) (cpp)

Leetcode 47. Permutations II (Medium) (cpp)

Tag: Backtracking

Difficulty: Medium

/*

47. Permutations II (Medium)

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

For example,
[1,1,2] have the following unique permutations:
[
[1,1,2],
[1,2,1],
[2,1,1]
]

*/
class Solution {
public:
vector<vector<int>> permuteUnique(vector<int>& nums) {
vector<vector<int>> res;
permuteUnique(res, nums, 0);
return res;
}
private:
void permuteUnique(vector<vector<int>>& res, vector<int>& nums, int index) {
if (index == nums.size()) {
res.push_back(nums);
return;
}
unordered_set<int> s;
for (int i = index; i < nums.size(); i++) {
if (s.find(nums[i]) == s.end()) {
swap(nums[i], nums[index]);
permuteUnique(res, nums, index + 1);
swap(nums[i], nums[index]);
s.insert(nums[i]);
}
}
}
};