Merge pull request #677 from RyouMon/master

优化 0059.螺旋矩阵II.md Python3解法

problems/0059.螺旋矩阵II.md

@@ -191,33 +191,48 @@ class Solution {
 
 python:
 
-```python
+```python3
 class Solution:
+
     def generateMatrix(self, n: int) -> List[List[int]]:
-        left, right, up, down = 0, n-1, 0, n-1
-        matrix = [ [0]*n for _ in range(n)]
-        num = 1
-        while left<=right and up<=down:
-            # 填充左到右
-            for i in range(left, right+1):
-                matrix[up][i] = num
-                num += 1
-            up += 1
-            # 填充上到下
-            for i in range(up, down+1):
-                matrix[i][right] = num
-                num += 1
-            right -= 1
-            # 填充右到左
-            for i in range(right, left-1, -1):
-                matrix[down][i] = num
-                num += 1
-            down -= 1
-            # 填充下到上
-            for i in range(down, up-1, -1):
-                matrix[i][left] = num
-                num += 1
+        # 初始化要填充的正方形
+        matrix = [[0] * n for _ in range(n)]
+
+        left, right, up, down = 0, n - 1, 0, n - 1
+        number = 1  # 要填充的数字
+
+        while left < right and up < down:
+
+            # 从左到右填充上边
+            for x in range(left, right):
+                matrix[up][x] = number
+                number += 1
+
+            # 从上到下填充右边
+            for y in range(up, down):
+                matrix[y][right] = number
+                number += 1
+
+            # 从右到左填充下边
+            for x in range(right, left, -1):
+                matrix[down][x] = number
+                number += 1
+
+            # 从下到上填充左边
+            for y in range(down, up, -1):
+                matrix[y][left] = number
+                number += 1
+
+            # 缩小要填充的范围
             left += 1
+            right -= 1
+            up += 1
+            down -= 1
+
+        # 如果阶数为奇数，额外填充一次中心
+        if n % 2:
+            matrix[n // 2][n // 2] = number
+
         return matrix
 ```