diff --git a/README.md b/README.md
index 8e31a95..f6e2df6 100644
--- a/README.md
+++ b/README.md
@@ -754,27 +754,32 @@ You'll get more graph practice in Skiena's book (see Books section below) and th
         - Just the videos - 41 (each are simple and each are short):
             - [x] https://www.youtube.com/watch?v=uzkc-qNVoOk&list=PLC58778F28211FA19
 
-- [ ] **NP and NP Complete**
+- [ ] **NP, NP-Complete and Approximation Algorithms**
     - Know about the most famous classes of NP-complete problems, such as traveling salesman and the knapsack problem,
         and be able to recognize them when an interviewer asks you them in disguise.
     - Know what NP-complete means.
     - [x] Computational Complexity: https://www.youtube.com/watch?v=moPtwq_cVH8&list=PLUl4u3cNGP61Oq3tWYp6V_F-5jb5L2iHb&index=23
-    - [ ] Simonson: 
+    - [ ] Simonson:
         - [x] https://youtu.be/qcGnJ47Smlo?list=PLFDnELG9dpVxQCxuD-9BSy2E7BWY3t5Sm&t=2939
-        - [ ] https://www.youtube.com/watch?v=e0tGC6ZQdQE&index=16&list=PLFDnELG9dpVxQCxuD-9BSy2E7BWY3t5Sm
+        - [x] https://www.youtube.com/watch?v=e0tGC6ZQdQE&index=16&list=PLFDnELG9dpVxQCxuD-9BSy2E7BWY3t5Sm
         - [ ] https://www.youtube.com/watch?v=fCX1BGT3wjE&index=17&list=PLFDnELG9dpVxQCxuD-9BSy2E7BWY3t5Sm
-    - [ ] CSE373 2012 - Lecture 23 - Introduction to NP-Completeness: https://youtu.be/KiK5TVgXbFg?list=PLOtl7M3yp-DV69F32zdK7YJcNXpTunF2b&t=1508
-    - [ ] CSE373 2012 - Lecture 24 - NP-Completeness Proofs: https://www.youtube.com/watch?v=27Al52X3hd4&index=24&list=PLOtl7M3yp-DV69F32zdK7YJcNXpTunF2b
-    - [ ] CSE373 2012 - Lecture 25 - NP-Completeness Challenge: https://www.youtube.com/watch?v=xCPH4gwIIXM&index=25&list=PLOtl7M3yp-DV69F32zdK7YJcNXpTunF2b
+        - [ ] https://www.youtube.com/watch?v=NKLDp3Rch3M&list=PLFDnELG9dpVxQCxuD-9BSy2E7BWY3t5Sm&index=18
+    - [ ] Skiena:
+        - [x] CSE373 2012 - Lecture 23 - Introduction to NP-Completeness: https://youtu.be/KiK5TVgXbFg?list=PLOtl7M3yp-DV69F32zdK7YJcNXpTunF2b&t=1508
+        - [ ] CSE373 2012 - Lecture 24 - NP-Completeness Proofs: https://www.youtube.com/watch?v=27Al52X3hd4&index=24&list=PLOtl7M3yp-DV69F32zdK7YJcNXpTunF2b
+        - [ ] CSE373 2012 - Lecture 25 - NP-Completeness Challenge: https://www.youtube.com/watch?v=xCPH4gwIIXM&index=25&list=PLOtl7M3yp-DV69F32zdK7YJcNXpTunF2b
     - [x] Complexity: P, NP, NP-completeness, Reductions: https://www.youtube.com/watch?v=eHZifpgyH_4&list=PLUl4u3cNGP6317WaSNfmCvGym2ucw3oGp&index=22
-    - [ ] Complexity: Approximation Algorithms: https://www.youtube.com/watch?v=MEz1J9wY2iM&list=PLUl4u3cNGP6317WaSNfmCvGym2ucw3oGp&index=24
+    - [x] Complexity: Approximation Algorithms: https://www.youtube.com/watch?v=MEz1J9wY2iM&list=PLUl4u3cNGP6317WaSNfmCvGym2ucw3oGp&index=24
     - [ ] Complexity: Fixed-Parameter Algorithms: https://www.youtube.com/watch?v=4q-jmGrmxKs&index=25&list=PLUl4u3cNGP6317WaSNfmCvGym2ucw3oGp
-    - Peter Norvik discusses solutions:
+    - Peter Norvik discusses suboptimal solutions to traveling salesman problem:
         - http://nbviewer.jupyter.org/url/norvig.com/ipython/TSP.ipynb
+    - Pages 1048 - 1140 in CLRS if you have it.
 
 - [ ] **Garbage collection**
     - [ ] Computer Science 61B - 2014-04-30: Garbage collection; Augmenting data str: https://www.youtube.com/watch?v=StdfeXaKGEc&list=PL-XXv-cvA_iAlnI-BQr9hjqADPBtujFJd&index=25
-    - [ ] https://www.youtube.com/playlist?list=PLO9y7hOkmmSGTy5z6HZ-W4k2y8WXF7Bff
+    - [ ] Garbage Collection is Good!: https://www.infoq.com/presentations/garbage-collection-benefits
+    - [ ] Compilers: https://www.youtube.com/playlist?list=PLO9y7hOkmmSGTy5z6HZ-W4k2y8WXF7Bff
+    - [ ] GC in Python: https://www.youtube.com/watch?v=iHVs_HkjdmI
 
 - [ ] **Caches**
     - [ ] LRU cache:
@@ -1211,7 +1216,9 @@ Some of mine (I already may know answer to but want their opinion or team perspe
 - [ ] **Parallel Programming**
     - https://www.coursera.org/learn/parprog1/home/week/1
     
-- [ ] Cryptography (see videos below)
+- [ ] Cryptography (also see videos below)
+    - [ ] Cryptography: Hash Functions: https://www.youtube.com/watch?v=KqqOXndnvic&list=PLUl4u3cNGP6317WaSNfmCvGym2ucw3oGp&index=30
+    - [ ] Cryptography: Encryptiom: https://www.youtube.com/watch?v=9TNI2wHmaeI&index=31&list=PLUl4u3cNGP6317WaSNfmCvGym2ucw3oGp
 
 - [ ] Entropy (see videos below)