C++ :

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#define gmax(a,b) ((a)>(b)?(a):(b))
#define fill(a,b) memset(a,b,sizeof(a))
#define MAXN 2000
#define MAXM 2000
using namespace std;
int n, m, k;
int a[MAXN][MAXM];
int s[MAXN][MAXM];
int ak[MAXN][MAXM];
int lu[MAXN][MAXM], ru[MAXN][MAXM], ld[MAXN][MAXM], rd[MAXN][MAXM];
int ans;
int main(){
 
    int i, j;
    scanf("%d %d %d", &n, &m, &k);
    for (i=1; i<n+1; i++){
        for (j=1; j<m+1; j++){
            scanf("%d", &a[i][j]);
            }
        }
    fill(s, 0);
    for (i=1; i<n+1; i++){
        for (j=1; j<m+1; j++){
            s[i][j] = s[i - 1][j] + s[i][j - 1] - s[i - 1][j - 1] + a[i][j];
            }
        }
    fill(ak, 0);
    for (i=k; i<n+1; i++){
        for (j=k; j<m+1; j++){
            ak[i][j] = s[i][j] - s[i - k][j] - s[i][j - k] + s[i - k][j - k];
            }
        }
    fill(lu, 0);
    for (i=k; i<n+1; i++){
        for (j=k; j<m+1; j++){
            lu[i][j] = ak[i][j];
            lu[i][j] = gmax(lu[i][j], lu[i - 1][j]);
            lu[i][j] = gmax(lu[i][j], lu[i][j - 1]);
            }
        }
    fill(ru, 0);
    for (i=k; i<n+1; i++){
        for (j=m-k+1; j; j--){
            ru[i][j] = ak[i][j + k - 1];
            ru[i][j] = gmax(ru[i][j], ru[i - 1][j]);
            ru[i][j] = gmax(ru[i][j], ru[i][j + 1]);
            }
        }
    fill(ld, 0);
    for (i=n-k+1; i; i--){
        for (j=k; j<m+1; j++){
            ld[i][j] = ak[i + k - 1][j];
            ld[i][j] = gmax(ld[i][j], ld[i + 1][j]);
            ld[i][j] = gmax(ld[i][j], ld[i][j - 1]);
            }
        }
    fill(rd, 0);
    for (i=n-k+1; i; i--){
        for (j=m-k+1; j; j--){
            rd[i][j] = ak[i + k - 1][j + k - 1];
            rd[i][j] = gmax(rd[i][j], rd[i + 1][j]);
            rd[i][j] = gmax(rd[i][j], rd[i][j + 1]);
            }
        }
    ans = 0;
    for (j=k; j+(k<<1)<m+1; j++){
        for (i=k; i<n+1; i++){
            int t = lu[n][j] + ak[i][j + k] + ru[n][j + k + 1];
            ans = gmax(ans, t);
            }
        }
    for (i=k; i+(k<<1)<n+1; i++){
        for (j=k; j<m+1; j++){
            int t = lu[i][m] + ak[i + k][j] + ld[i + k + 1][m];
            ans = gmax(ans, t);
            }
        }
    for (j=k; j+k<m+1; j++){
        for (i=k; i+k<n+1; i++){
            int t = lu[n][j] + ru[i][j + 1] + rd[i + 1][j + 1];
            ans = gmax(ans, t);
            }
        }
    for (j=k; j+k<m+1; j++){
        for (i=k; i+k<n+1; i++){
            int t = lu[i][j] + ld[i + 1][j] + rd[1][j + 1];
            ans = gmax(ans, t);
            }
        }
    for (i=k; i+k<n+1; i++){
        for (j=k; j+k<m+1; j++){
            int t = lu[i][n] + ld[i + 1][j] + rd[i + 1][j + 1];
            ans = gmax(ans, t);
            }
        }
 
    for (i=k; i+k<n+1; i++){
        for (j=k; j+k<m+1; j++){
            int t = lu[i][j] + ru[i][j + 1] + ld[i + 1][m];
            ans = gmax(ans, t);
            }
        }
 
 
    printf("%d\n", ans);
 
 
    return 0;
    }

Java :

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class Main {
static int map[][];
static int sum[][];
static int kk[][];
static int leftup[][];
static int rightup[][];
static int leftdown[][];
static int rightdown[][];
static int max(int a, int b) {
return a>b?a: b;
}
static void print(int arr[][]) {
for(int i=0;i<arr.length;i++) {
for(int j=0;j<arr[i].length;j++) {
System.out.print(arr[i][j]+" ");
}
System.out.println();
}
System.out.println();
}
public static void main(String args[]) throws IOException {
int M,N,K;
//Scanner in = new Scanner(System.in);
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
//录入数据
String cs[] = br.readLine().split(" ");
M=Integer.valueOf(cs[0]);
N=Integer.valueOf(cs[1]);
K=Integer.valueOf(cs[2]);
//M=in. nextInt();
//N=in. nextInt();
//K=in. nextInt();
int m = M-K+1;
int n = N-K+1;
map = new int[M+1][N+1];
for(int i=1;i<=M;i++) {
cs = br.readLine().split(" ");
for(int j=1;j<=N;j++) {
//map[i][j]=in.nextInt();
map[i][j]=Integer. valueOf(cs[j-1]);
}
}
//用前缀和计算 sum
sum = new int[M+1][N+1];
for(int i=1;i<=M;i++) {
for(int j=1;j<=N;j++) {
sum[i][j]=sum[i-1][j]+sum[i][j-1]-sum[i-1][j-1]+map[i]
[j];
}
}
//用前缀和计算 kk
kk = new int[m][n];
for(int i=K;i<=M;i++) {
for(int j=K;j<=N;j++) {
kk[i-K][j-K]=sum[i][j]-sum[i-K][j]-sum[i][j-K]+sum[i-K]
[j-K];
}
}
//计算四个方向的 max
leftup = new int[m][n];
rightup = new int[m][n];
leftdown = new int[m][n];
rightdown = new int[m][n];
leftup[0][0]=kk[0][0];
for(int i=1;i<m;i++)
leftup[i][0]=max(kk[i][0], leftup[i-1][0]);
for(int j=1;j<n;j++)
leftup[0][j]=max(kk[0][j], leftup[0][j-1]);
for(int i=1;i<m;i++) {
for(int j=1;j<n;j++) {
leftup[i][j]=max(kk[i][j], max(leftup[i-1][j], leftup[i]
[j-1]));
}
}

rightup[0][n-1]=kk[0][n-1];
for(int i=1;i<m;i++)
rightup[i][n-1]=max(kk[i][n-1], rightup[i-1][n-1]);
for(int j=n-2;j>=0;j--)
rightup[0][j]=max(kk[0][j], rightup[0][j+1]);
for(int i=1;i<m;i++) {
for(int j=n-2;j>=0;j--) {
rightup[i][j]=max(kk[i][j], max(rightup[i-1][j], rightup[i][j+1]));
}
}
leftdown[m-1][0]=kk[m-1][0];
for(int i=m-2;i>=0;i--)
leftdown[i][0]=max(kk[i][0], leftdown[i+1][0]);
for(int j=1;j<n;j++)
leftdown[m-1][j]=max(kk[m-1][j], leftdown[m-1][j-1]);
for(int i=m-2;i>=0;i--) {
for(int j=1;j<n;j++) {
leftdown[i][j]=max(kk[i][j], max(leftdown[i][j-1], leftdown[i+1][j]));
}
}
rightdown[m-1][n-1]=kk[m-1][n-1];
for(int i=m-2;i>=0;i--)
rightdown[i][n-1]=max(kk[i][n-1], rightdown[i+1][n-1]);
for(int j=n-2;j>=0;j--)
rightdown[m-1][j]=max(kk[m-1][j], rightdown[m-1][j+1]);
for(int i=m-2;i>=0;i--) {
for(int j=n-2;j>=0;j--) {
rightdown[i][j]=max(kk[i][j], max(rightdown[i+1][j], rightdown[i][j+1]));
}
}
//计算六种情况
int ans=0;
//一
for(int j=0;j<n-2*K;j++) {
for(int i=0;i<m;i++) {
ans = max(ans, leftup[m-1][j]+kk[i][j+K]+rightup[m-1][j
+K+K]);
}
}
//|
for(int i=0;i<m-2*K;i++) {
for(int j=0;j<n;j++) {
ans = max(ans, leftup[i][n-1]+kk[i+K][j]+leftdown[i+K+K]
[n-1]);
}
}
//左
for(int i=0;i<m-K;i++) {
for(int j=0;j<n-K;j++) {
ans = max(ans, leftup[m-1][j]+rightup[i][j+K]+rightdown
[i+K][j+K]);
}
}
//右
for(int i=0;i<m-K;i++) {
for(int j=n-1;j-K>0;j--) {
ans = max(ans, leftup[i][j-K]+leftdown[i+K][j-K]+rightup[m-1][j]);
}
}
//上
for(int i=0;i<m-K;i++) {
for(int j=0;j<n-K;j++) {
ans = max(ans, leftup[i][n-1]+leftdown[i+K][j]+rightdown[i+K][j+K]);
}
}
//下
for(int i=K;i<m;i++) {
for(int j=0;j<n-K;j++) {
ans = max(ans, leftup[i-K][j]+rightup[i-K][j+K]+leftdown[i][n-1]);
}
}
System. out.println(ans);
}
}