🏣 Clean up for arxiv

book/ebook_src/builtin_structures/rotate_NxN.py

@@ -0,0 +1,30 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+def rotate_NxN(m):
+    n = len(m)
+    for layer in range(n//2):
+        first = layer
+        last = n - 1 - layer
+        for i in range(first, last):
+            offset = i - first
+            top = m[first][i]
+            m[first][i] = m[last-offset][first]
+            m[last-offset][first] = m[last][last-offset]
+            m[last][last-offset] = m[i][last]
+            m[i][last] = top
+    return m
+
+
+
+def main():
+    m = [[1,2],[3,4]]
+    mr = [[3,1],[4,2]]
+    assert(rotate_NxN(m) == mr)
+    m2 = [[1,2,3],[4,5,6],[7,8,9]]
+    print(rotate_NxN(m2))
+
+if __name__ == '__main__':
+    main()
+