add solution: rotate-image

Author: dusunax

rotate-image/dusunax.py

@@ -0,0 +1,77 @@
+'''
+# 48. Rotate Image
+
+rotate 2d matrix 90 degree in place.
+👉 transpose matrix and reverse each row.
+
+- original matrix
+1 2 3
+4 5 6
+7 8 9
+
+- transpose matrix (swap i, j) (flip diagonally)
+1 4 7
+2 5 8
+3 6 9
+
+- reverse each row (horizontal flip)
+7 4 1
+8 5 2
+9 6 3
+'''
+class Solution:
+    '''
+    TC: O(n^2)
+    SC: O(1)
+    '''
+    def rotate(self, matrix: List[List[int]]) -> None:
+        n = len(matrix)
+
+        for i in range(n):
+            for j in range(i, n):
+                matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j]
+        
+        for i in range(n):
+            matrix[i].reverse()
+
+'''
+# 💡 other rotate in-place examples
+
+## rotate 180 degree
+
+### solution A. reverse each column (vertical flip) & reverse each row (horizontal flip)
+
+```python
+def rotate180(matrix: List[List[int]]) -> None:
+  n = len(matrix)
+  matrix.reverse()
+
+  for i in range(n):
+    matrix[i].reverse()
+```
+
+### solution B. (after transpose, reverse each row (horizontal flip)) * 2.
+
+90 degree * 2 = 180 degree
+
+```python
+def rotate180(matrix: List[List[int]]) -> None:
+  rotate90(matrix)
+  rotate90(matrix)
+```
+
+## rotate -90 degree
+
+after transpose, reverse each column (vertical flip)
+
+```python
+def rotate90CCW(matrix):
+    n = len(matrix)
+
+    for i in range(n):
+        for j in range(i, n):
+            matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j]
+
+    matrix.reverse()
+```
+'''