BNU 26349——Cards——————【区间dp】

#include<bits/stdc++.h>
using namespace std;
typedef long long INT;
#define min(a,b) ((a)<(b)?(a):(b))
#define max(a,b) ((a)>(b)?(a):(b))
const int maxn=1e3+20;
int dp[maxn][maxn][2];
int a[maxn];
int main(){
    int n;
    while(scanf("%d",&n)!=EOF){
        int sum=0;
        for(int i=1;i<=n;i++){
            scanf("%d",&a[i]);
            sum+=a[i];
        }
        for(int i=1;i<=n;i++){
            dp[i][i][0]=a[i];
            dp[i][i][1]=a[i];
        }
        for(int i=1;i<n;i++){
            dp[i][i+1][0]=a[i];
            dp[i][i+1][1]=a[i+1];
        }
        int tm00,tm01,tm11,tm10;
        for(int k=2;k<n;k++){
            for(int i=1;i+k<=n;i++){
                tm00=a[i]+max(dp[i+2][i+k][0],dp[i+2][i+k][1]);
                tm01=a[i]+max(dp[i+1][i+k-1][0],dp[i+1][i+k-1][1]);
                dp[i][i+k][0]=min(tm00,tm01);//后手肯定会让先手这次只能取到上次取的两个最大值中的最小值
                tm11=a[i+k]+max(dp[i][i+k-2][0],dp[i][i+k-2][1]);
                tm10=a[i+k]+max(dp[i+1][i+k-1][0],dp[i+1][i+k-1][1]);
                dp[i][i+k][1]=min(tm11,tm10);
            }
        }
        int tmp=max(dp[1][n][0],dp[1][n][1]);
        printf("%d\n",2*tmp-sum);
    }
    return 0;
}