Treats for the Cows 记忆化搜索

#include<stdio.h>#include<string.h>int hash[2005][2005];int treat[2005];int num;int dfs(int head,int tail,int n);int main(){    int i,k;    while(scanf("%d",&num)!=EOF)    {        memset(hash,0,sizeof(hash));        for(i=0;i<num;i++)            scanf("%d",&treat[i]);        k=dfs(0,num-1,1);        printf("%d\n",k);    }    return 0;}int dfs(int head,int tail,int n){    int max=0,k1,k2;    if(n>num) return 0;    if(hash[head][tail]) return hash[head][tail];    k1=n*treat[head]+dfs(head+1,tail,n+1);    k2=n*treat[tail]+dfs(head,tail-1,n+1);    max=k1>=k2?k1:k2;    hash[head][tail]=max;    return max;}

DP我不会，我只会DFS+记忆化来剪枝。。。。。