【洛谷P1006】传纸条

双线程dp

f [ i ] [ j ] [ k ] [ l ] 表示 走到 （i，j），返回时走到（k，l）时的（总）最大价值

 1 #include<cstdio>
 2 #include<cstring>
 3 using namespace std;
 4 const int N=52;
 5 int f[N][N][N][N],a[N][N],n,m;
 6 int max(int x,int y){
 7     return x>y?x:y;
 8 }
 9 int main(){
10     int p,q;
11     scanf("%d %d",&n,&m);
12     for (int i=1;i<=n;i++)
13         for (int j=1;j<=m;j++)
14             scanf("%d",&a[i][j]);
15     for (int i=1;i<=n;i++)
16     for (int j=1;j<=m;j++)
17     for (int k=1;k<=n;k++)
18     for (int l=1;l<=m;l++){
19         p=max(f[i-1][j][k-1][l],f[i-1][j][k][l-1]);
20         q=max(f[i][j-1][k-1][l],f[i][j-1][k][l-1]);
21         f[i][j][k][l]=max(p,q);
22         f[i][j][k][l]+=a[i][j]+a[k][l];
23         if (i==k&&j==l)
24             f[i][j][k][l]-=a[i][j];
25     }
26     printf("%d",f[n][m][n][m]);
27     return 0;
28 }

STD