Update README.md

Author: zenglekidd

README.md

@@ -38,14 +38,14 @@ Total: 111 / 111
 
 Stage 4
 From a reference [here](https://leetcode.com/discuss/interview-experience/904425/facebook-amazon-apple-google-nyc-oct-2020-offerofferghostedoffer)
-- [ ] Tackle a topic at once and then go back and solve a bunch of related problems.
+- [x] Tackle a topic at once and then go back and solve a bunch of related problems.
+  Topics:
+  - [ ] Buy and Sell Stock
+  - [ ] Recursion
+  - [ ] 2D Array connectivities
+  
 - [ ] Made sure to do a lot of mock interviews. Almost 1 mock interview every other weekend or so.
 
-
-Topics:
-- [ ] Recursion
-- [ ] 2D Array connectivities
-
 ## Paper
 - [x] 'Programming pearls: algorithm design techniques' by Jon Bentley (Sep. 1984 Vol. 27 No. 9 Communications of the ACM P885)