90 Subsets II

90. Subsets II

1. Question

Given a collection of integers that might contain duplicates, nums, return all possible subsets (the power set).
Note: The solution set must not contain duplicate subsets.
For example, Ifnums=[1,2,2], a solution is:
[
[2],
[1],
[1,2,2],
[2,2],
[1,2],
[]
]

2. Implementation

(1) Backtracking
class Solution {
public List<List<Integer>> subsetsWithDup(int[] nums) {
List<List<Integer>> res = new ArrayList<>();
List<Integer> subset = new ArrayList<>();
Arrays.sort(nums);
getSubsets(nums, 0, subset, res);
return res;
}
public void getSubsets(int[] nums, int start, List<Integer> subset, List<List<Integer>> res) {
res.add(new ArrayList<>(subset));
for (int i = start; i < nums.length; i++) {
if (i > start && nums[i - 1] == nums[i]) {
continue;
}
subset.add(nums[i]);
getSubsets(nums, i + 1, subset, res);
subset.remove(subset.size() - 1);
}
}
}

3. Time & Space Complexity

Backtracking: 时间复杂度O(2^n), 空间复杂度O(2^n)