LeetCode 329. Longest Increasing Path in a Matrix（矩阵内的最长递增路径）

原题网址：https://leetcode.com/problems/longest-increasing-path-in-a-matrix/

Given an integer matrix, find the length of the longest increasing path.

From each cell, you can either move to four directions: left, right, up or down. You may NOT move diagonally or move outside of the boundary (i.e. wrap-around is not allowed).

Example 1:

nums = [
  [9,9,4],
  [6,6,8],
  [2,1,1]
]

Return 4
The longest increasing path is [1, 2, 6, 9].

Example 2:

nums = [
  [3,4,5],
  [3,2,6],
  [2,2,1]
]

Return 4
The longest increasing path is [3, 4, 5, 6]. Moving diagonally is not allowed.

方法：递归+动态规划。

public class Solution {
    private int[] ro = {-1, 1, 0, 0};
    private int[] co = {0, 0, -1, 1};
    private int find(int[][] matrix, boolean[][] visited, int[][] path, int row, int col) {
        if (visited[row][col]) return path[row][col];
        path[row][col] = 1;
        for(int i=0; i<4; i++) {
            int r = row + ro[i];
            int c = col + co[i];
            if (r>=0 && r=0 && c matrix[r][c]) {
                path[row][col] = Math.max(path[row][col], find(matrix, visited, path, r, c)+1);
            }
        }
        visited[row][col] = true;
        return path[row][col];
    }
    public int longestIncreasingPath(int[][] matrix) {
        if (matrix == null || matrix.length == 0 || matrix[0].length == 0) return 0;
        boolean[][] visited = new boolean[matrix.length][matrix[0].length];
        int[][] path = new int[matrix.length][matrix[0].length];
        int max = 0;
        for(int i=0; i