59. Spiral Matrix II

Author: YuriSpiridonov

Medium/59.SpiralMatrixII.py

@@ -0,0 +1,76 @@
+"""
+    Given a positive integer n, generate an n x n matrix filled with elements 
+    from 1 to n^2 in spiral order.
+
+    Example:
+    Input: n = 3
+    Output: [[1,2,3],[8,9,4],[7,6,5]]
+
+    Example:
+    Input: n = 1
+    Output: [[1]]
+
+    Constraints:
+        - 1 <= n <= 20
+"""
+#Difficulty: Medium
+#20 / 20 test cases passed.
+#Runtime: 28 ms
+#Memory Usage: 14.4 MB
+
+#Runtime: 28 ms, faster than 84.67% of Python3 online submissions for Spiral Matrix II.
+#Memory Usage: 14.4 MB, less than 26.01% of Python3 online submissions for Spiral Matrix II.
+
+class Solution:
+    def generateMatrix(self, n: int) -> List[List[int]]:
+        row = 0
+        col = 0
+        val = 1
+        matrix = [[None for i in range(n)] for j in range(n)]
+        reverse = False
+        while val <= n**2:
+            if not reverse:
+                while col < n:
+                    if matrix[row][col] is None:
+                        matrix[row][col] = val
+                        col += 1
+                        val += 1
+                    else:
+                        break
+                col -= 1
+                if matrix[row][col] is not None or col == n:
+                    row += 1
+                while row < n:
+                    if matrix[row][col] is None:
+                        matrix[row][col] = val
+                        row += 1
+                        val += 1
+                    else:
+                        break
+                row -= 1
+                if matrix[row][col] is not None or row == n:
+                    col -= 1
+                reverse = not reverse
+            else:
+                while col >= 0:
+                    if matrix[row][col] is None:
+                        matrix[row][col] = val
+                        col -= 1
+                        val += 1
+                    else:
+                        break
+                if matrix[row][col] is not None or col < 0:
+                    col += 1
+                    row -= 1
+                while row >= 0:
+                    if matrix[row][col] is None:
+                        matrix[row][col] = val
+                        row -= 1
+                        val += 1
+                    else:
+                        break
+                if matrix[row][col] is not None or row < 0:
+                    col += 1
+                    row += 1
+                reverse = not reverse
+        return matrix