Week 15: Rotate Image Solution

Author: doh6077

rotate-image/doh6077.py

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+# https://leetcode.com/problems/rotate-image/
+# 48. Rotate Image
+class Solution:
+    def rotate(self, matrix: List[List[int]]) -> None:
+        """
+        Do not return anything, modify matrix in-place instead.
+        """
+        # First Try - Thought process:
+        # group values by column index (j) to rebuild rows
+        # Brute force: create an extra 2D matrix and then copy it back into matrix
+        # Needs optimization: this approach uses extra space
+        matrix_result = [[] for _ in range(len(matrix))]
+        for i in reversed(matrix):
+            for j, value in enumerate(i):
+                matrix_result[j].append(value)
+        for r in range(len(matrix)):
+            matrix[r] = matrix_result[r]
+        
+        # Youtube Solution - Transpose Operation + hr 
+        # Swap i, js
+        n = len(matrix)
+        for i in range(n):
+            for j in range(i + 1, n):
+                matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j]
+
+        # Reflection
+        for i in range(n):
+            for j in range(n // 2):
+                matrix[i][j], matrix[i][n - j - 1] = matrix[i][n - j - 1], matrix[i][j]