矩阵最长递增路径-DFS

class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     * 递增路径的最大长度
     * @param matrix int整型vector<vector<>> 描述矩阵的每个数
     * @return int整型
     */
    vector<vector<int>> dirs = {{0, -1}, {-1, 0}, {0, 1}, {1, 0}};
    int solve(vector<vector<int> >& matrix) {
        // write code here
        if (matrix.empty() || matrix[0].empty())
            return 0;
        int res = 1, m = matrix.size(), n = matrix[0].size();
        vector<vector<int>> dp(m, vector<int>(n, 0));
        for (int i = 0; i < m; ++i)
        {
            for (int j = 0; j < n; ++j)
            {
                res = max(res, dfs(matrix, dp, i, j));
            }
        }
        return res;
    }

    int dfs(vector<vector<int>> &matrix, vector<vector<int>> &dp, int i, int j)
    {
        if (dp[i][j])
            return dp[i][j];
        int mx = 1, m = matrix.size(), n = matrix[0].size();
        for (auto a : dirs)
        {
            int x = i + a[0], y = j + a[1];
            if (x < 0 || x >= m || y < 0 || y >= n || matrix[x][y] <= matrix[i][j])
                continue;
            int len = 1 + dfs(matrix, dp, x, y);
            mx = max(mx, len);
        }
        dp[i][j] = mx;
        return mx;
    }
};