78 Subsets

78. Subsets

1. Question

Given a set of distinct integers,nums, return all possible subsets (the power set).
Note:The solution set must not contain duplicate subsets.
For example, Ifnums=[1,2,3], a solution is:
[
[3],
[1],
[2],
[1,2,3],
[1,3],
[2,3],
[1,2],
[]
]

2. Implementation

(1) Backtracking
class Solution {
public List<List<Integer>> subsets(int[] nums) {
List<List<Integer>> res = new ArrayList<>();
List<Integer> subset = new ArrayList<>();
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++) {
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)