题目

题目链接：
https://www.nowcoder.com/practice/c333d551eb6243e0b4d92e37a06fbfc9

思路

递归实现：先升序排序；然后每个位置i为起点，i到最后的数，要么被选择，要么被放弃
递归实现；注意结果集，长度短的子集放前面

参考答案Java

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param S int整型一维数组
     * @return int整型ArrayList<ArrayList<>>
     */
    public ArrayList<ArrayList<Integer>> subsets (int[] S) {
       Arrays.sort(S);
            ArrayList<ArrayList<Integer>> ans = new ArrayList<>();
            Map<Integer,ArrayList<ArrayList<Integer>>> help = new HashMap<>();
            ans.add(new ArrayList<>());
            dfs(S,0,new ArrayList<Integer>(),help);
            //System.out.println(help);
            for (int i = 1; i <=S.length ; i++) {
                ArrayList<ArrayList<Integer>> arrayLists = help.get(i);

                for (ArrayList<Integer> arrayList : arrayLists) {
                   // System.out.println(arrayList);
                    ans.add(arrayList);
                }
            }
            return ans;
        }

        public void dfs(int[] arr,int index,ArrayList<Integer> path,Map<Integer,ArrayList<ArrayList<Integer>>> help ){
            if(path.size()>0){
                //ans.add(new ArrayList<>(path));
                int mkey = path.size();
                if(!help.containsKey(mkey))
                    help.put(mkey,new ArrayList<>());

                help.get(mkey).add(new ArrayList<>(path));
            }

            for (int i = index; i <arr.length ; i++) {
                path.add(arr[i]);
                dfs(arr,i+1,path,help);
                path.remove(path.size()-1); //恢复现场
            }
        }
}

参考答案Go

package main
import "sort"


/**
 * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
 *
 *
 * @param S int整型一维数组
 * @return int整型二维数组
 */
func subsets(S []int) [][]int {
	//dfs
	sort.Ints(S)
	imap := map[int][][]int{}
	imap[0] = make([][]int, 0)
	path := []int{}
	dfs(S, 0, path, imap)

	ans := [][]int{}
	ans = append(ans, []int{})
	//fmt.Println(imap)
	for i := 0; i <= len(S); i++ {
		nexts := imap[i]
		for _, next := range nexts {
			ans = append(ans, next)
		}
	}

	return ans
}

func dfs(arr []int, index int, path []int, imap map[int][][]int) {
	//fmt.Println(path)
	if len(path) > 0 {
		mkey := len(path)
		_, ok := imap[mkey]
		if !ok {
			imap[mkey] = [][]int{}
		}
		pathbak := make([]int, mkey)
		for k := 0; k < mkey; k++ {
			pathbak[k] = path[k]
		}
		imap[mkey] = append(imap[mkey], pathbak)
	}

	for i := index; i < len(arr); i++ {
		path = append(path, arr[i])
		dfs(arr, i+1, path, imap)

		pathbak := path[:len(path)-1]
		path = pathbak //恢复现场
	}
}

参考答案PHP

<?php


/**
 * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
 *
 * 
 * @param S int整型一维数组 
 * @return int整型二维数组
 */
function subsets( $S )
{
        sort($S);
    $path = array();
    $map = array();
    dfs($S,0,$path,$map);

    $ans = [0=>[]];
    for($i=1;$i<=count($S);$i++){
        $nexts =  $map[$i];
        foreach ($nexts as $next){
          $ans[count($ans)] = $next;
        }
    }

    return $ans;
}

function dfs($arr,$index,$path,&$map){
    if(count($path) >0 ){
        $mkey = count($path);
        if(!isset($map[$mkey])){
            $map[$mkey] =array();
        }

        $pathbak=array();
        for($m=0;$m<$mkey;$m++){
            $pathbak[$m] = $path[$m];
        }

        $cnt= count($map[$mkey]);
        $map[$mkey][$cnt] = $pathbak;
    }


    for($i=$index;$i<count($arr);$i++){
        array_push($path,$arr[$i]);
        dfs($arr,$i+1,$path,$map);
        array_pop($path); //恢复现场
    }
}