59.Spiral Matrix II
===

###### tags: `Medium`,`Array`,`Matrix`

[59. Spiral Matrix II](https://leetcode.com/problems/spiral-matrix-ii/)

### 題目描述

Given a positive integer `n`, generate an `n x n` `matrix` filled with elements from `1` to n^2^ in spiral order.

### 範例

**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

### 解答
#### Python
偷懶拿昨天的 code 改寫

class Solution:
    def generateMatrix(self, n: int) -> List[List[int]]:
        directions = [(0, 1), (1, 0), (0, -1), (-1, 0)]
        d = 0
        sx, sy = 0, 0
        matrix = [[0] * n for _ in range(n)]
        fill_val = 1
        matrix[sx][sy] = fill_val

        while fill_val < n * n:
            dx, dy = directions[d % 4]
            nx, ny = sx + dx, sy + dy

            if 0 <= nx < n and 0 <= ny < n and not matrix[nx][ny]:
                fill_val += 1
                matrix[nx][ny] = fill_val
                sx, sy = nx, ny
            else:
                d += 1

        return matrix

> [name=Ron Chen][time=Wed, May 10, 2023]

### Reference

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