纯动态规划。
注意初始化为-INF
#include<stdio.h>
#include<algorithm>
#include<iostream>
#include<string.h>
#define INF 99999999
#define max3(a,b,c) max(max(a,b),c)
using namespace std;
int n,m,i,j;
int map[1010][1010];
int dp[1010][1010];
int main()
{while(~scanf("%d%d",&n,&m)){for(i=1;i<=n;i++){for(j=1;j<=m;j++){scanf("%d",&map[i][j]);}}if(map[1][1]==-1){cout<<"cannot arrive."<<endl;continue;}for(i=1;i<=n;i++)for(j=1;j<=m;j++)dp[i][j]=-INF;dp[1][1]=map[1][1];for(i=1;i<=n;i++){for(j=1;j<=m;j++){if(map[i][j]==-1)continue;if(i-1>=1&&j-2>=1&&map[i-1][j-2]!=-1){dp[i][j]=max(dp[i][j],dp[i-1][j-2]+map[i][j]);}if(i-2>=1&&j-1>=1&&map[i-2][j-1]!=-1){dp[i][j]=max(dp[i][j],dp[i-2][j-1]+map[i][j]);}}}int maxx;maxx=0;for(i=1;i<=n;i++)maxx=max(maxx,dp[i][m]);for(i=1;i<=m;i++)maxx=max(maxx,dp[n][i]);if(maxx<=0)cout<<"cannot arrive."<<endl;else cout<<maxx<<endl;}return 0;
}