【LeetCode】78. Subsets

1.题目描述

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

给定一组不含重复元素的整数数组 nums，返回该数组所有可能的子集（幂集）。

Note: The solution set must not contain duplicate subsets.

说明：解集不能包含重复的子集。

Example:

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

2.Solutions

public List<List<Integer>> subsets(int[] nums) {
    List<List<Integer>> list = new ArrayList<>();
    Arrays.sort(nums);
    backtrack(list, new ArrayList<>(), nums, 0);
    return list;
}

private void backtrack(List<List<Integer>> list , 
                       List<Integer> tempList, int [] nums, int start){
    list.add(new ArrayList<>(tempList));
    for(int i = start; i < nums.length; i++){
        tempList.add(nums[i]);
        backtrack(list, tempList, nums, i + 1);
        tempList.remove(tempList.size() - 1);
    }
}

I drew an ugly but clear pic about how backtracking works. Once nums[i] arrived at end, remove the last element and go back to last level until all possible solutions are stored.

位运算：My solution using bit manipulation

（完）