add rotate image

Author: tg123

rotate-image/README.md

@@ -1,4 +1,62 @@
+## [Transpose](http://en.wikipedia.org/wiki/Transpose) then Reverse
 
-## TODO 
-  * write down thinking
+You must know this method, or it is difficult.
 
+```
++---+---+
+| 1 | 2 |
++---+---+
+| 3 | 4 |
++---+---+
+```
+
+Transpose: reflect the matrix over the main diagonal.
+
+
+```
+Before
+
++          
+ +---+---+
+ | + | 2 |
+ +---+---+
+ | 3 | + |
+ +---+---+
+          +
+
+After
+
++          
+ +---+---+
+ | 1 | 3 |
+ +---+---+
+ | 2 | 4 |
+ +---+---+
+          +
+```
+
+Reverse: exchange each number along the vertical line in the middle
+
+```
+Before
+
+    |
++---+---+
+| 1 | 3 |
++---+---+
+| 2 | 4 |
++---+---+
+    |
+
+
+After
+
+    |
++---+---+
+| 3 | 1 |
++---+---+
+| 4 | 2 |
++---+---+
+    |
+
+```