题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=4597
感觉很不错的区间DP，又做了一遍，感觉自己对边界的处理还是很欠缺
代码：
1 #include<iostream> 2 #include<cstdio> 3 #include<cstring> 4 #include<cstdlib> 5 using namespace std; 6 #define maxn 21 7 int sum1[maxn]; 8 int sum2[maxn]; 9 int q1[maxn]; 10 int q2[maxn]; 11 int n; 12 int dp[maxn][maxn][maxn][maxn]; 13 int dfs(int s1, int e1,int s2,int e2) 14 { 15 int tmp1,tmp2; 16 int ans; 17 if(s1==0 && s2==0 && e1==0 && e2==0) return dp[s1][e1][s2][e2]=0; 18 if(dp[s1][e1][s2][e2]>=0) return dp[s1][e1][s2][e2]; 19 if(s1==0 && e1==0 && s2==e2) return dp[0][0][s2][e2]=q2[s2]; 20 if(s1==e1 && s2==0 && e2==0) return dp[s1][e1][0][0]=q1[s1]; 21 if(s1==0 && e1 ==0) 22 ans=max(q2[s2]+sum2[e2]-sum2[s2]-dfs(0,0,s2+1,e2),q2[e2]+sum2[e2-1]-sum2[s2-1]-dfs(0,0,s2,e2-1)); 23 else 24 if(s2==0 && e2 ==0) 25 ans=max(q1[s1]+sum1[e1]-sum1[s1]-dfs(s1+1,e1,0,0),q1[e1]+sum1[e1-1]-sum1[s1-1]-dfs(s1,e1-1,0,0)); 26 else 27 if(s1==e1 && s2==e2) 28 ans=max(q1[s1],q2[s2]); 29 else 30 if(s1==e1) 31 { 32 tmp1=max(q2[s2]+sum2[e2]-sum2[s2]+q1[s1]-dfs(s1,e1,s2+1,e2),q2[e2]+sum2[e2-1]-sum2[s2-1]+q1[s1]-dfs(s1,e1,s2,e2-1)); 33 tmp2=max(tmp1,q1[s1]+sum2[e2]-sum2[s2-1]-dfs(0,0,s2,e2)); 34 ans=max(tmp1,tmp2); 35 } 36 else 37 if(s2==e2) 38 { 39 tmp1=max(q1[s1]+sum1[e1]-sum1[s1]+q2[s2]-dfs(s1+1,e1,s2,e2),q1[e1]+sum1[e1-1]-sum1[s1-1]+q2[s2]-dfs(s1,e1-1,s2,e2)); 40 tmp2=max(tmp1,q2[s2]+sum1[e1]-sum1[s1-1]-dfs(s1,e1,0,0)); 41 ans=max(tmp1,tmp2); 42 } 43 else 44 { 45 tmp1=max(q1[s1]+sum2[e2]-sum2[s2-1]+sum1[e1]-sum1[s1]-dfs(s1+1,e1,s2,e2),q1[e1]+sum2[e2]-sum2[s2-1]+sum1[e1-1]-sum1[s1-1]-dfs(s1,e1-1,s2,e2)); 46 tmp2=max(q2[s2]+sum2[e2]-sum2[s2]+sum1[e1]-sum1[s1-1]-dfs(s1,e1,s2+1,e2),q2[e2]+sum2[e2-1]-sum2[s2-1]+sum1[e1]-sum1[s1-1]-dfs(s1,e1 ,s2,e2-1)); 47 ans=max(tmp1,tmp2); 48 } 49 return dp[s1][e1][s2][e2]=ans; 50 } 51 int main() 52 { 53 int t; 54 scanf("%d",&t); 55 while(t--) 56 { 57 scanf("%d",&n); 58 sum1[0]=sum2[0]=0; 59 for(int i=1;i<=n;i++) 60 { 61 scanf("%d",&q1[i]); 62 sum1[i]=sum1[i-1]+q1[i]; 63 } 64 for(int i=1;i<=n;i++) 65 { 66 scanf("%d",&q2[i]); 67 sum2[i]=sum2[i-1]+q2[i]; 68 } 69 memset(dp,-1,sizeof(dp)); 70 dp[1][n][1][n]=dfs(1,n,1,n); 71 cout<<dp[1][n][1][n]<<endl; 72 } 73 return 0; 74 }