NOIP 2008 传纸条

#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
int a[51][51],d[105][51][51];
int main(int argc, char *argv[])
{
	int n,m,i,j,k;
	cin>>n>>m;
	for(i=1;i<=n;i++)
	for(j=1;j<=m;j++)
	cin>>a[i][j];
	memset(d,0,sizeof(d));
	for(k=2;k<=m+n-1;k++)  //枚举步数和两条路径的行数，且第k步时x+y==k+1,所以只需以行坐标为状态 
	for(i=1;i<=min(k,n);i++)
	for(j=1;j<=min(n,k);j++)
	{d[k][i][j]=max(max(d[k-1][i][j],d[k-1][i-1][j]),max(d[k-1][i][j-1],d[k-1][i-1][j-1]));
	if(i==j&&k-i+1<=m) d[k][i][j]+=a[i][k-i+1];
	else {if(k-i+1<=m) d[k][i][j]+=a[i][k-i+1]; if(k-j+1<=m) d[k][i][j]+=a[j][k-j+1];}
    }	
	cout<<d[m+n-1][n][n]<<endl;//输出应该是d[m+n-1][n][n],不小心写成d[m+n-1][n][m]
	return 0;
}