题解 | #矩阵最长递增路径#

import java.util.*;


public class Solution {

    private int[][] dirs = new int[][] {
        {-1, 0}, {1, 0}, {0, -1}, {0, 1}
    };


    /**
     * 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整型二维数组 描述矩阵的每个数
     * @return int整型
     */
    public int solve (int[][] matrix) {
        // write code here
        if (matrix == null || matrix.length < 1|| matrix[0] == null || matrix[0].length < 1) {
            return 0;
        }
        int res = 0;
        int n = matrix.length;
        int m = matrix[0].length;
        int[][] dp = new int[n + 1][m + 1];
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                res = Math.max(res, dfs(matrix, dp, i, j));
            }
        }
        return res;
    }

    private int dfs(int[][] matrix, int[][] dp, int i, int j) {
        if (dp[i][j] != 0) {
            return dp[i][j];
        }
        int n = matrix.length;
        int m = matrix[0].length;
        dp[i][j]++;
        for (int k = 0; k < 4; k++) {
            int row = i + dirs[k][0];
            int col = j + dirs[k][1];
            if (row >= 0 && row < n && col >= 0 && col < m && matrix[row][col] > matrix[i][j]) {
                dp[i][j] = Math.max(dp[i][j], dfs(matrix, dp, row, col) + 1);
            }
        }
        return dp[i][j];
    }
}