329. 矩阵中的最长递增路径

class Solution {
public:
   
    int longestIncreasingPath(vector<vector<int>> &matrix)
    {
        if (matrix.size() == 0)
            return 0;
       
        int xmax = matrix.size();
        int ymax = matrix[0].size();

        int ** tmp = new int*[xmax];

        for (int i = 0; i < xmax; i++)
        {
            tmp[i] = new int[ymax];
            for (int j = 0; j < ymax; j++)
            {
                tmp[i][j] = 0;
            }
        }

        int maxlen = 0;
        for (int i = 0; i < xmax; i++)
        {
            for (int j = 0; j < ymax; j++)
            {
                maxlen = max(maxlen, dp(matrix, i, j, tmp, xmax, ymax));
            }
        }

        return maxlen;
    }

    int dp(vector<vector<int>> &matrix, int i, int j, int ** tmp, int xmax, int ymax)
    {
        if (tmp[i][j] != 0)
        {
            return tmp[i][j];
        }

        int xdir[4] = { 1, 0, -1, 0 };
        int ydir[4] = { 0, 1, 0, -1 };

        tmp[i][j] = 1;

        for (int k = 0; k < 4; k++)
        {
            int x = i + xdir[k];
            int y = j + ydir[k];

            if (x >= 0 && x < xmax && y >= 0 && y < ymax && matrix[x][y]>matrix[i][j])
            {
                int maxlen = max(dp(matrix, x, y, tmp, xmax, ymax) + 1, tmp[i][j]);
                tmp[i][j] = maxlen;
            }
        }

        return tmp[i][j];
    }
};