add pernumtation

tg123 · tg123 · commit 3a2c9c1207bf · 2014-08-17T23:07:06.000+08:00
diff --git a/permutations/README.md b/permutations/README.md
@@ -1,4 +1,13 @@
+## Definition
+
+
+```
+
+permute(num) = empty                                num is empty
+               num                                  num has only one element
+               n + permute(num - n)    [n in num]   otherwise
+               
+```
+
 
-## TODO 
-  * write down thinking
 
