78. Subsets

Given a set of distinct integers, nums, return all possible subsets.

Note: The solution set must not contain duplicate subsets.

For example,
If nums = [1,2,3], a solution is:

[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

在leetcode的topsulotion里有这类题的一套模板： A general approach to backtracking questions in Java (Subsets, Permutations, Combination Sum, Palindrome Partitioning) 。会发现用这套模板解体，基本就是变一两行的事情，代码如下：

public class Solution {
    public List<List<Integer>> subsets(int[] nums) {
        List<List<Integer>> result = new ArrayList<List<Integer>>();
        Arrays.sort(nums);
        backtrack(result, new ArrayList<Integer>(), nums, 0);
        return result;
    }
    public void backtrack(List<List<Integer>> list, List<Integer> tempList, int[] nums, int start) {
        list.add(new ArrayList<Integer>(tempList));
        for (int i = start; i < nums.length; i ++) {
            tempList.add(nums[i]);
            backtrack(list, tempList, nums, i + 1);
            tempList.remove(tempList.size() - 1);
        }
    }
}