记录详情

#include<bits/stdc++.h>
using namespace std;
//___________________________________________________________________________________________________________________________
const int N = 3009;
long long a[N][N];
int n, m;
long long dp[N][N][3];//0 : up; 1 : down; 2 : left; (from)
int main(){
	memset(dp, 0xc0, sizeof(dp));
	scanf("%d%d", &n, &m);
	for(int i = 1; i <= n; i++){
		for(int j = 1; j <= m; j++){
			scanf("%lld", &a[i][j]);
		}
	}
	dp[1][1][0] = dp[1][1][1] = dp[1][1][2] = a[1][1];
	for(int i = 2; i <= m; i++) dp[i][1][0] = dp[i - 1][1][0] + a[i][1];
	for(int j = 2; j <= m; j++){
		for(int i = 1; i <= n; i++) dp[i][j][2] = max(max(dp[i][j - 1][0], dp[i][j - 1][1]), dp[i][j - 1][2]) + a[i][j];
		for(int i = 1; i <= n; i++) dp[i][j][0] = max(dp[i - 1][j][0], dp[i - 1][j][2]) + a[i][j];
		for(int i = n; i >= 1; i--) dp[i][j][1] = max(dp[i + 1][j][1], dp[i + 1][j][2]) + a[i][j];
	}
	printf("%lld\n", max(dp[n][m][0], dp[n][m][2]));
	return 0;
}