hdu 1258 Sum It Up

离散化+深搜。

对给出的n个数排序，然后离散，求出每个数有多少个，然后递归判断每个数出现多少次时 能使和等于sum，需要注从大数开始深搜。。

代码：

# include<stdio.h>
# include<string.h>
# include<stdlib.h>
int a[20],b[20],c[20],sum,ans,flag,ys;
int cmp(const void *a,const void *b)
{
    return *(int *)b - *(int *)a;
}
void dfs(int i)
{
    int j,k,h;
    for(j=b[i];j>=0;j--)
    {
        ans+=a[i]*j;
        c[i]=j;
        if(ans>sum)
        {
            ans-=a[i]*j;
            continue;
        }
            if(ans==sum)
            {
                flag=0;
                for(k=1;k<=i;k++)
                {
                    for(h=1;h<=c[k];h++)
                    {
                        if(flag==0) {printf("%d",a[k]);flag=1;}
                        else printf("+%d",a[k]);
                    }
                }
                printf("\n");
                ans-=a[i]*j;
                continue;
            }
            if(i==ys) {ans-=a[i]*j;return;}
        dfs(i+1);
        ans-=a[i]*j;
    }
}
int main()
{
    int i,n;
    while(scanf("%d%d",&sum,&n)!=EOF)
    {
        if(sum==0 && n==0) break;
        for(i=1;i<=n;i++)
            scanf("%d",&a[i]);
        qsort(a+1,n,sizeof(a[1]),cmp);
        memset(b,0,sizeof(b));
        ys=1;
        b[ys]=1;
        for(i=2;i<=n;i++)
        {
            if(a[i]==a[i-1]) b[ys]++;
            else
            {
                ys++;
                a[ys]=a[i];
                b[ys]=1;
            }
        }
        ans=0;
        flag=0;
        printf("Sums of %d:\n",sum);
        dfs(1);
        if(flag==0) printf("NONE\n");
    }
    return 0;
}