https://leetcode.com/problems/longest-increasing-path-in-a-matrix/
Given an m x n integers matrix, return __the length of the longest increasing path in __matrix. From each cell, you can either move in four directions: left, right, up, or down. You may not move diagonally or move outside the boundary (i.e., wrap-around is not allowed).
Example 1:
Input: matrix = [[9,9,4],[6,6,8],[2,1,1]] Output: 4 Explanation: The longest increasing path is [1, 2, 6, 9].
Example 2:
Input: matrix = [[3,4,5],[3,2,6],[2,2,1]] Output: 4 Explanation: The longest increasing path is [3, 4, 5, 6]. Moving diagonally is not allowed.
Example 3:
Input: matrix = [[1]] Output: 1
Constraints:
m == matrix.length
n == matrix[i].length
1 <= m, n <= 200
0 <= matrix[i][j] <= 231 - 1
- code
class Solution:
def longestIncreasingPath(self, matrix: List[List[int]]) -> int:
m, n = len(matrix), len(matrix[0])
direction = [(-1, 0), (1, 0), (0, 1), (0, -1)]
memo = [[0] * n for _ in range(m)]
def dfs(x, y):
if memo[x][y] != 0: return memo[x][y]
cur_max = 0
for dx, dy in direction:
nx, ny = x + dx, y + dy
if 0 <= nx < m and 0 <= ny < n and matrix[nx][ny] > matrix[x][y]:
cur_max = max(cur_max, dfs (nx, ny))
memo[x][y] = cur_max + 1
return memo[x][y]
res = 0
for i in range(m):
for j in range(n):
res = max(res, dfs(i, j))
return res