solve(w15): 48. Rotate Image

Author: seungriyou

rotate-image/seungriyou.py

@@ -0,0 +1,30 @@
+# https://leetcode.com/problems/rotate-image/
+
+from typing import List
+
+class Solution:
+    def rotate(self, matrix: List[List[int]]) -> None:
+        """
+        Do not return anything, modify matrix in-place instead.
+        """
+        """
+        [Complexity]
+            - TC: O(n^2) (diagonal = n * (n - 1) / 2)
+            - SC: O(1)
+
+        [Approach]
+            clockwise rotation을 in-place로 하려면 다음의 순서로 수행한다.
+                1. matrix reverse (by row)
+                2. matrix transpose (diagonal)
+        """
+
+        n = len(matrix)
+
+        # 1. matrix reverse (by row)
+        for r in range(n // 2):
+            matrix[r], matrix[n - r - 1] = matrix[n - r - 1], matrix[r]
+
+        # 2. matrix transpose (diagonal)
+        for r in range(n):
+            for c in range(r):
+                matrix[r][c], matrix[c][r] = matrix[c][r], matrix[r][c]