一、题目内容

二、题解

解法1：

思路

全排列+数组长度排序

代码

public class Solution {
    ArrayList<ArrayList<Integer>> ans;
    ArrayList<Integer> path;
    int[] nums;
    public ArrayList<ArrayList<Integer>> subsets(int[] S) {
        ans = new ArrayList();
        path = new ArrayList();
        this.nums = S;
        recur(0);
        //sortByLen(ans,1,ans.size()-1);
        return ans;
    }
    private void recur(int x){
        ans.add(new ArrayList(path));
        for(int i = x;i<nums.length;i++){
            path.add(nums[i]);
            recur(i+1);
            path.remove(path.size()-1);
        }
    }
    Collections.sort(new ArrayList<T>(),new Comparable<Integer>(){
            @Override
            public int compareTo(Integer o) {
                return 0;
            }
        });
    private void sortByLen(ArrayList<ArrayList<Integer>> ans,int low,int high){
        if(low>=high){
            return;
        }
        int partation = partation(ans,low,high);
        sortByLen(ans,low,partation-1);
        sortByLen(ans,partation+1,high);
    }
    private int partation(ArrayList<ArrayList<Integer>> ans,int low,int high){
        int left = low,right = high;
        int target = ans.get(left).size();
        ArrayList<Integer> temp = ans.get(left);
        while(left<right){
            while(left<right&&ans.get(right).size()>target){
                right--;
            }
            ans.set(left,ans.get(right));
            while(left<right&&ans.get(left).size()<target){
                left++;
            }
            ans.set(right,ans.get(left));
        }
        ans.set(left,temp);
        return left;
    }
}