LeetCode - Subsets II
Problem description
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.
Example:
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Input: [1,2,2]
Output:
[
[2],
[1],
[1,2,2],
[2,2],
[1,2],
[]
]
Analysis
The idea is to skip other duplicates after the backtrack. So that we can consider the subsets only once.
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class Solution {
public List<List<Integer>> subsetsWithDup(int[] nums) {
List<List<Integer>> res = new ArrayList<>();
Arrays.sort(nums);
backtrack(res, new ArrayList<>(), 0, nums);
return res;
}
void backtrack(List<List<Integer>> res, List<Integer> list, int start, int[] nums){
res.add(new ArrayList<>(list));
if (start == nums.length){
return;
}
for (int i = start; i< nums.length; i++){
list.add(nums[i]);
backtrack(res, list, i+1, nums);
list.remove(list.size() - 1);
while(i + 1 < nums.length && nums[i] == nums[i + 1]){
i++;
}
}
}
}
What to improve
- skip duplicates must be after the backtrack so that we can use previous information.