【棋盘类DP】传纸条

http://codevs.cn/problem/1169/

#include<iostream>using namespace std;int a[100][100];int dp[55][55][55][55];int main(){int n,m;cin>>n>>m;for (int i=1;i<=n;i++)for (int j=1;j<=m;j++)cin>>a[i][j];for (int x1=1;x1<=n;x1++)for (int y1=1;y1<=m;y1++)for (int x2=1;x2<=n;x2++)for (int y2=1;y2<=m;y2++){dp[x1][y1][x2][y2]=max(dp[x1][y1][x2][y2],dp[x1-1][y1][x2-1][y2]);dp[x1][y1][x2][y2]=max(dp[x1][y1][x2][y2],dp[x1-1][y1][x2][y2-1]);dp[x1][y1][x2][y2]=max(dp[x1][y1][x2][y2],dp[x1][y1-1][x2-1][y2]);dp[x1][y1][x2][y2]=max(dp[x1][y1][x2][y2],dp[x1][y1-1][x2][y2-1]);dp[x1][y1][x2][y2]+=a[x1][y1];if (x1==x2&&y1==y2&&((x1==n&&y1==m)||(x1==1&&y1==1)))continue;else if (x1==x2&&y1==y2)dp[x1][y1][x2][y2]=0;else dp[x1][y1][x2][y2]+=a[x2][y2];}cout<<dp[n][m][n][m];}