O(n^2) time and O(1) space using transpose and reverse double pass.

Author: 149ps

Diff for: 48. Rotate Image/48. Rotate Image.py

@@ -0,0 +1,55 @@
+"""
+You are given an n x n 2D matrix representing an image.
+
+Rotate the image by 90 degrees (clockwise).
+
+Note:
+
+You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.
+
+Example 1:
+
+Given input matrix =
+[
+  [1,2,3],
+  [4,5,6],
+  [7,8,9]
+],
+
+rotate the input matrix in-place such that it becomes:
+[
+  [7,4,1],
+  [8,5,2],
+  [9,6,3]
+]
+Example 2:
+
+Given input matrix =
+[
+  [ 5, 1, 9,11],
+  [ 2, 4, 8,10],
+  [13, 3, 6, 7],
+  [15,14,12,16]
+],
+
+rotate the input matrix in-place such that it becomes:
+[
+  [15,13, 2, 5],
+  [14, 3, 4, 1],
+  [12, 6, 8, 9],
+  [16, 7,10,11]
+]
+"""
+
+
+class Solution:
+    def rotate(self, matrix: List[List[int]]) -> None:
+        """
+        Do not return anything, modify matrix in-place instead.
+        """
+        for i in range(len(matrix)):
+            for j in range(i, len(matrix)):
+                matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j]
+        for i in range(len(matrix)):
+            matrix[i].reverse()
+