hdu 4597 记忆化搜索

思路：定义一个四维状态的数组，记录每个状态先手的最优值。

#include<iostream>
#include<algorithm>
#include<cmath>
#include<cstring>
#include<cstdio>
#define Maxn 30
using namespace std;
int ans[Maxn][Maxn][Maxn][Maxn],suma[Maxn],sumb[Maxn];
void init()
{
    memset(ans,0,sizeof(ans));
    memset(suma,0,sizeof(suma));
    memset(sumb,0,sizeof(sumb));
}
inline int Max(int a,int b,int c,int d)
{
    a=a>b?a:b;
    c=c>d?c:d;
    return a>c?a:c;
}
int dfs(int l,int r,int l1,int r1)
{
    if(l>r&&l1>r1) return 0;
    if(ans[l][r][l1][r1]) return ans[l][r][l1][r1];
    int levsum=suma[r]-suma[l-1]+sumb[r1]-sumb[l1-1];
    int ans1=0,ans2=0,ans3=0,ans4=0;
    if(l<=r){
        ans1=levsum-dfs(l+1,r,l1,r1);
        ans2=levsum-dfs(l,r-1,l1,r1);
    }
    if(l1<=r1){
        ans3=levsum-dfs(l,r,l1+1,r1);
        ans4=levsum-dfs(l,r,l1,r1-1);
    }
    return ans[l][r][l1][r1]=Max(ans1,ans2,ans3,ans4);
}
int main()
{
    int n,i,j,t,x;
    scanf("%d",&t);
    while(t--){
        init();
        scanf("%d",&n);
        for(i=1;i<=n;i++){
            scanf("%d",&x);
            suma[i]=suma[i-1]+x;
        }
        for(i=1;i<=n;i++){
            scanf("%d",&x);
            sumb[i]=sumb[i-1]+x;
        }
        printf("%d\n",dfs(1,n,1,n));
    }
    return 0;
}