59. Spiral Matrix II

Problem

Given a positive integer n, generate an n x n matrix filled with elements from 1 to n² in spiral order.

https://leetcode.cn/problems/spiral-matrix-ii/

Example 1:

Input: n = 3
Output: [[1,2,3],[8,9,4],[7,6,5]]

Example 2:

Input: n = 1
Output: [[1]]

Constraints:

1 <= n <= 20

Test Cases

    python
    
  
class Solution:
    def generateMatrix(self, n: int) -> List[List[int]]:

solution_test.py下载完整源码

    py
    
  
import pytest

from solution import Solution


@pytest.mark.parametrize('n, expected', [
    (3, [[1,2,3],[8,9,4],[7,6,5]]),
    (1, [[1]]),
])
@pytest.mark.parametrize('sol', [Solution()])
def test_solution(sol, n, expected):
    assert sol.generateMatrix(n) == expected

Thoughts

跟 54. Spiral Matrix 类似，完全一样的遍历顺序，只是读出还是写入的区别。直接把代码搬过来，把 res[idx] = matrix[i][j] 替换成 matrix[i][j] = idx + 1，m 改成 n，基本就可以了。

Code

solution.py下载完整源码

    py
    
  
class Solution:
    def generateMatrix(self, n: int) -> list[list[int]]:
        matrix = [[0] * n for _ in range(n)]
        steps = ((0, 1), (1, 0), (0, -1), (-1, 0)) # →, ↓, ←, ↑
        limits = [n, n - 1] # ↔︎, ↕
        i = 0
        j = -1
        dir = 0
        move = 0
        for idx in range(1, n * n + 1):
            i += steps[dir][0]
            j += steps[dir][1]
            matrix[i][j] = idx
            move += 1
            if move == limits[dir & 1]:
                limits[dir & 1] -= 1
                dir = (dir + 1) % 4
                move = 0

        return matrix

#Problem

#Test Cases

#Thoughts

#Code

Problem

Test Cases

Thoughts

Code