题解 | #集合的所有子集(一)# 脑瘫暴力

import java.util.*;


public class Solution {
    Map<Integer, ArrayList<Integer>> resultMap = new HashMap<>();
    // 数组哈希值
    public int arrHash(ArrayList<Integer> arr) {
        if(arr.size() == 0){
            return -9999;
        }
        int len = arr.size();
        int sum = 0;
        for (int i = 0; i < len; i++) {
            sum = (sum+1) * 10 + arr.get(i);
        }
        System.out.println("数组"  + arr.toString() + "  |  哈希值:" + sum);
        return sum;
    }

    void dfs(int[] arr, int idx, ArrayList<Integer> t) {
        resultMap.put(arrHash(t), t);
        if (idx >= arr.length) return;
        // 加入
        ArrayList<Integer> newArr2 = new ArrayList<>(t);
        newArr2.add(arr[idx]);
        dfs(arr, idx + 1, newArr2);
        // 不加入
        ArrayList<Integer> newArr1 = new ArrayList<>(t);
        dfs(arr, idx + 1, newArr1);

    }

    public ArrayList<ArrayList<Integer>> subsets (int[] S) {
        Arrays.sort(S);
        dfs(S, 0, new ArrayList<>());
        ArrayList<ArrayList<Integer>> returnData = new ArrayList<>();
        for (Integer key : resultMap.keySet()) {
            returnData.add(resultMap.get(key));
        }

        Collections.sort(returnData, new Comparator<ArrayList<Integer>>() {
            public int compare(ArrayList<Integer> p1, ArrayList<Integer> p2) {
                if(p1.size() == p2.size()){
                    return p1.get(p1.size()-1) < p2.get(p2.size()-1) ? -1:1;
                }
                 return p1.size() < p2.size() ? -1:1;
            }
        });

        return returnData;
    }
}

优化？什么优化？