class Solution {
int n, m;
bool valid(const int x, const int y) { return x >= 0 && x < n && y >= 0 && y < m; }
int dfs(vector<vector<int>> &grid, const int x, const int y) {
static const int dir[] = {1, 0, -1, 0, 1};
int res = 0;
grid[x][y] = -grid[x][y];
for (int k = 0; k < 4; k++) {
const int i = x + dir[k + 1];
const int j = y + dir[k];
if (!valid(i, j) || grid[i][j] <= 0) continue;
res = max(res, dfs(grid, i, j));
}
grid[x][y] = -grid[x][y];
return grid[x][y] + res;
}
public:
int getMaximumGold(vector<vector<int>> &grid) {
n = grid.size(), m = grid[0].size();
int res = 0;
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++)
res = max(res, dfs(grid, i, j));
}
return res;
}
};