JAVA解Leetcode 90题 Subsets

• • 题目描述
  • 问题解答

题目描述

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:

Input: [1,2,2]
Output:
[
  [2],
  [1],
  [1,2,2],
  [2,2],
  [1,2],
  []
]

这道题与78题的差别在于输入数组有重复数字，因此在解题的时候需要判断重复并进行剪枝。

问题解答

Runtime: 1 ms, faster than 99.75% of Java online submissions for Subsets II.
Memory Usage: 39.3 MB, less than 40.45% of Java online submissions for Subsets II.

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