add wildcard matching

Author: tg123

wildcard-matching/README.md

@@ -1,4 +1,62 @@
+## Convert to [Regular Expression Matching](../regular-expression-matching)
 
-## TODO 
-  * write down thinking
+ * `?` -> `.`
+ * `*` -> `.*`
 
+This should work, yet, it exceeds the time limited. 
+
+## Checkpoint / Timemachine
+
+On modern OS, you can go back to some time you saved if your OS meets some problem.
+such technology also can be used to solve this problem.
+
+```
+    S
+ 
+[ a a b ]
+ 
+[ a * b * ]
+ 
+    P
+ 
+ 
+P is *, save current state. 
+```
+
+`P` goes on to next
+
+```
+
+This state means * matches nothing
+
+    S
+ 
+[ a a b ]
+ 
+[ a * b * ]
+ 
+      P
+
+```
+
+a mismatch found, `P != S`, so rollback to checkpoint.
+
+```
+This state means * matches a
+
+      S
+ 
+[ a a b ]
+ 
+[ a * b * ]
+ 
+      P
+```
+
+Each `*` will save to a checkpoint, and retry from nothing until a match is found.
+
+
+### Remaining tail
+
+Sometimes, `S` meets the end, but the `P` not. 
+In this case, just to check remaining chars in `P` are all `*`.