HDu 1258 Sum It Up (还是DFS)

Sum It Up

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 5691    Accepted Submission(s): 2967

Problem Description

Given a specified total t and a list of n integers, find all distinct sums using numbers from the list that add up to t. For example, if t=4, n=6, and the list is [4,3,2,2,1,1], then there are four different sums that equal 4: 4,3+1,2+2, and 2+1+1.(A number can be used within a sum as many times as it appears in the list, and a single number counts as a sum.) Your job is to solve this problem in general.

 

Input

The input will contain one or more test cases, one per line. Each test case contains t, the total, followed by n, the number of integers in the list, followed by n integers x1,...,xn. If n=0 it signals the end of the input; otherwise, t will be a positive integer less than 1000, n will be an integer between 1 and 12(inclusive), and x1,...,xn will be positive integers less than 100. All numbers will be separated by exactly one space. The numbers in each list appear in nonincreasing order, and there may be repetitions.

 

Output

For each test case, first output a line containing 'Sums of', the total, and a colon. Then output each sum, one per line; if there are no sums, output the line 'NONE'. The numbers within each sum must appear in nonincreasing order. A number may be repeated in the sum as many times as it was repeated in the original list. The sums themselves must be sorted in decreasing order based on the numbers appearing in the sum. In other words, the sums must be sorted by their first number; sums with the same first number must be sorted by their second number; sums with the same first two numbers must be sorted by their third number; and so on. Within each test case, all sums must be distince; the same sum connot appear twice.

 

Sample Input

   
   
   
   

    
    
    
    4 6 4 3 2 2 1 1
5 3 2 1 1
400 12 50 50 50 50 50 50 25 25 25 25 25 25
0 0
   
   
   
   

 

Sample Output

   
   
   
   

    
    
    
    Sums of 4:
4
3+1
2+2
2+1+1
Sums of 5:
NONE
Sums of 400:
50+50+50+50+50+50+25+25+25+25
50+50+50+50+50+25+25+25+25+25+25
   
   
   
   

 

Source

浙江工业大学第四届大学生程序设计竞赛

原题链接:http://acm.hdu.edu.cn/showproblem.php?pid=1258

思路:先把输入的数据镜像排序,从大到小依次搜索.
去重是关键!

AC代码:

#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
int sum,n;
int a[20];
int ans[20];
bool flag;
bool cmp(int x,int y)
{
    return x>y;
}
void DFS(int x,int num,int start,int endd)//将要搜索的值,目前的和,开始位置,结束位置
{
    if(num>sum)
        return;
    if(num==sum)
    {
        cout<<ans[0];
        for(int i=1;i<endd;i++)
            cout<<"+"<<ans[i];
        cout<<endl;
        flag=true;
    }
    for(int i=start;i<n;i++)
    {
        ans[endd]=a[i];
        DFS(a[i],num+a[i],i+1,endd+1);
        while(i+1<n&&a[i]==a[i+1])//搜索完毕后，若下一个搜索的数仍与当前相同，则跳过直至不相同
            i++;
    }
}
int main()
{
    while(cin>>sum>>n)
    {
        if(sum==0&&n==0)
            break;
        int sum2=0;
        for(int i=0; i<n; i++)
        {
            cin>>a[i];
            sum2+=a[i];
        }
        cout<<"Sums of "<<sum<<":"<<endl;
        if(sum2<sum)
        {
           cout<<"NONE"<<endl;
           continue;
        }
        sort(a,a+n,cmp);
        flag=false;
        DFS(0,0,0,0);
        if(!flag)
        {
            cout<<"NONE"<<endl;
        }
    }
    return 0;
}