429B - Working out - CodeForces Solution

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

#define ll   long long
#define fast ios_base::sync_with_stdio(0); cin.tie(0);  cout.tie(0);
#define el '\n'
using namespace std;
using namespace __gnu_pbds;
typedef tree<int, null_type, less<>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;

const int N = 1e3 + 7;
const int MOD = 1e9 + 7;

int dx[] = {1, -1, 0, 0, -1, -1, 1, 1};
int dy[] = {0, 0, 1, -1, 1, -1, 1, -1};



// think very carefully before writing a line of code //
// enjoy the problems //
// never focus on performance during a contest //

int dp[N][N][4];
int A[N][N];
int n, m;


void doWork() {
    cin >> n >> m;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            cin >> A[i][j];
        }
    }
    // coming from 1,1 and moving left and down
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            dp[i][j][0] = A[i][j] + max(dp[i - 1][j][0], dp[i][j - 1][0]);
        }
    }
    // coming from n, 1 and moving up and right
    for (int i = n; i >= 1; i--) {
        for (int j = 1; j <= m; j++) {
            dp[i][j][1] = A[i][j] + max(dp[i + 1][j][1], dp[i][j - 1][1]);
        }
    }
    // coming from n, m and moving up and left
    for (int i = n; i >= 1; i--) {
        for (int j = m; j >= 1; j--) {
            dp[i][j][2] = A[i][j] + max(dp[i + 1][j][2], dp[i][j + 1][2]);
        }
    }
    // coming from 1, m and moving left and down
    for (int i = 1; i <= n; i++) {
        for (int j = m; j >= 1; j--) {
            dp[i][j][3] = A[i][j] + max(dp[i - 1][j][3], dp[i][j + 1][3]);
        }
    }

    int ans = 0;

    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            if (i - 1 >= 1 && i + 1 <= n && j - 1 >= 1 && j + 1 <= m) {
                ans = max(ans, dp[i - 1][j][0] + dp[i + 1][j][2] + dp[i][j + 1][3] + dp[i][j - 1][1]);
                ans = max(ans, dp[i - 1][j][3] + dp[i + 1][j][1] + dp[i][j + 1][2] + dp[i][j - 1][0]);
            }
        }
    }
    cout << ans;

}

signed main() {
    fast
//    freopen("snakes.in", "r", stdin);
//    freopen("snakes.out", "w", stdout);
    int testcases = 1;
//    cin >> testcases;
    for (int i = 1; i <= testcases; i++) {
        doWork();
    }
}