HDU1258 Sum it up

Sum it up

题意：给定一个数sum,和n个数，求sum可以由这n个数里面的那几个数的和表示。

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.

注意：输入，输出要求比较高，另外不能有重复。

​ 递归的时候应该及时退出。

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

#include<cstdio>#include<iostream>int sum,n;int flag=0;int a[20],ans[20];void  dfs(int sums,int cut,int x)//sums代表当前的和，cut代表ans里的[1,cut),x代表a中的第x个数{    if(sums==sum){        for(int i=1;i<cut;i++){            flag=1;            if(i==cut-1)                printf("%d\n",ans[i]);            else                printf("%d+",ans[i]);        }        return ;    }//如果结果sums==sum按格式输出ans 并且flag=1;    int t=-1;    for(int i=x;i<=n;i++){        if(t!=a[i]){            ans[cut]=a[i];            t=a[i];//避免重复            dfs(sums+a[i],cut+1,i+1);        }    }//    return ;//递归要有结束条件，不能是return;}int main (){    while(scanf("%d %d",&sum,&n),n||sum)    {        for(int i=1;i<=n;i++)            scanf("%d",&a[i]);        flag=0;        printf("Sums of %d:\n",sum);        dfs(0,1,1);        if(flag==0)            printf("NONE\n");    }    return 0;}