砝码称重(dfs)

 搜索顺序：搜n个砝码，每个砝码有三种可能，完成一个方案回溯

 

 

过掉50%代码1：（Set自带去重，香的嘞）

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.math.BigInteger;
import java.util.*;



public class Main
{
    static PrintWriter pw = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
    static int N = (int)1e5 + 10;
    static int n;
    static int w[] = new int[N];
    static Set<Integer> set = new HashSet<>();

    // 搜索顺序：搜n个砝码，每个砝码有三种可能，完成一个方案回溯
    static void dfs(int cur_num, int weight) // 当前的状态，选了多少个砝码，重量是多少
    {
        if(cur_num == n + 1) // cur_num偏移到n + 1,判断方案
        {
            // 重量是整的，丢到set去重
            if(weight > 0)   set.add(weight);
            return;
        }

        // cur_num + 1既代表当前的砝码数量，也代表w的下标
        dfs(cur_num + 1,weight + w[cur_num + 1]); // 砝码放左边
        dfs(cur_num + 1, weight); // 砝码放中间
        dfs(cur_num + 1,weight - w[cur_num + 1]); // 砝码放右边
    }

    public static void main(String[] args ) throws IOException
    {
        n = rd.nextInt();
        for(int i = 1 ; i <= n ; i ++)  w[i] = rd.nextInt();

        dfs(0,0); // 选了多少个砝码，重量是多少

        pw.println(set.size());
        pw.flush();
    }
}

class rd
{
    static BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
    static StringTokenizer tokenizer = new StringTokenizer("");

    static String nextLine() throws IOException  { return reader.readLine(); }

    static String next() throws IOException
    {
        while (!tokenizer.hasMoreTokens())  tokenizer = new StringTokenizer(reader.readLine());
        return tokenizer.nextToken();
    }

    static int nextInt() throws IOException  { return Integer.parseInt(next()); }

    static double nextDouble() throws IOException { return Double.parseDouble(next()); }

    static long nextLong() throws IOException  { return Long.parseLong(next());}

    static BigInteger nextBigInteger() throws IOException
    {
        BigInteger d = new BigInteger(rd.nextLine());
        return d;
    }
}

class PII
{
    int x,y;
    public PII(int x ,int y)
    {
        this.x = x;
        this.y = y;
    }
}

过掉50%代码2：（st数组去重）

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.math.BigInteger;
import java.util.*;



public class Main
{
    static PrintWriter pw = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
    static int N = (int)1e6 + 10;
    static int w[] = new int[N];
    static boolean st[] = new boolean[N];

    static int n;
    static int res;

    static void dfs(int k,int sum) // 表示k个砝码，重量是sum
    {
        if(k > n) // 选完n个砝码
        {
            if(sum > 0 &&  !st[sum]) // 判断选出来的n个砝码是否没被标记过，如没标记则答案加1
            {
                res ++;
                st[sum] = true;
            }
            return;
        }
        dfs(k + 1,sum - w[k]);
        dfs(k + 1,sum);
        dfs(k + 1, sum + w[k]);
    }

    public static void main(String[] args ) throws IOException
    {
        n = rd.nextInt();
        for(int i = 1 ; i <= n ; i ++)  w[i] = rd.nextInt();

        dfs(0,0);

        pw.println(res);
        pw.flush();
    }
}

class rd
{
    static BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
    static StringTokenizer tokenizer = new StringTokenizer("");

    static String nextLine() throws IOException  { return reader.readLine(); }

    static String next() throws IOException
    {
        while (!tokenizer.hasMoreTokens())  tokenizer = new StringTokenizer(reader.readLine());
        return tokenizer.nextToken();
    }

    static int nextInt() throws IOException  { return Integer.parseInt(next()); }

    static double nextDouble() throws IOException { return Double.parseDouble(next()); }

    static long nextLong() throws IOException  { return Long.parseLong(next());}

    static BigInteger nextBigInteger() throws IOException
    {
        BigInteger d = new BigInteger(rd.nextLine());
        return d;
    }
}

class PII
{
    int x,y;
    public PII(int x ,int y)
    {
        this.x = x;
        this.y = y;
    }
}