Leetcode(78) Subsets

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Description

Given a set of distinct integers, nums, return all possible subsets (the power set).

Note: The solution set must not contain duplicate subsets.

Example:

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Input: nums = [1,2,3]
Output:
[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

解法

这道题与之前combination那题基本解法一样，采用深度优先遍历，用开始参数向后搜索确保不重复，注意搜索完成后的回溯。

具体代码如下：

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class Solution {
    List<List<Integer>> res = new ArrayList<>();
    List<Integer> tmp = new ArrayList<>();

    public List<List<Integer>> subsets(int[] nums) {
        int n = nums.length;
        for (int i = 0; i <= n; i++) {
            helper(nums, 0, i);
        }
        return res;
    }

    void helper(int[] nums, int start, int len) {
        if (tmp.size() == len) {
            List<Integer> add = new ArrayList<>();
            for (int i = 0; i < tmp.size(); i++) {
                add.add(tmp.get(i));
            }
            res.add(add);
            return;
        }
        for (int i = start; i < nums.length; i++) {
            tmp.add(nums[i]);
            helper(nums, i + 1, len);
            tmp.remove((Integer) nums[i]);
        }
    }
}