Added Norvik NP complete, added disclaimer on Skiena videos.

README.md

@@ -713,9 +713,10 @@ You'll get more graph practice in Skiena's book (see Books section below) and th
  
 - [ ] **Dynamic Programming**
     - [ ] Videos:
+        - the Skiena videos can be hard to follow since he sometimes uses the whiteboard, which is too small to see
         - [x] Skiena: CSE373 2012 - Lecture 19 - Introduction to Dynamic Programming: https://youtu.be/Qc2ieXRgR0k?list=PLOtl7M3yp-DV69F32zdK7YJcNXpTunF2b&t=1718
         - [x] Skiena: CSE373 2012 - Lecture 20 - Edit Distance: https://youtu.be/IsmMhMdyeGY?list=PLOtl7M3yp-DV69F32zdK7YJcNXpTunF2b&t=2749
-        - [ ] Skiena: CSE373 2012 - Lecture 21 - Dynamic Programming Examples: https://youtu.be/o0V9eYF4UI8?list=PLOtl7M3yp-DV69F32zdK7YJcNXpTunF2b&t=406
+        - [x] Skiena: CSE373 2012 - Lecture 21 - Dynamic Programming Examples: https://youtu.be/o0V9eYF4UI8?list=PLOtl7M3yp-DV69F32zdK7YJcNXpTunF2b&t=406
         - [ ] Skiena: CSE373 2012 - Lecture 22 - Applications of Dynamic Programming: https://www.youtube.com/watch?v=dRbMC1Ltl3A&list=PLOtl7M3yp-DV69F32zdK7YJcNXpTunF2b&index=22
         - [x] Simonson: Dynamic Programming 0 (starts at 59:18): https://youtu.be/J5aJEcOr6Eo?list=PLFDnELG9dpVxQCxuD-9BSy2E7BWY3t5Sm&t=3558
         - [x] Simonson: Dynamic Programming I - Lecture 11: https://www.youtube.com/watch?v=0EzHjQ_SOeU&index=11&list=PLFDnELG9dpVxQCxuD-9BSy2E7BWY3t5Sm
@@ -760,6 +761,8 @@ You'll get more graph practice in Skiena's book (see Books section below) and th
     - [ ] 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
     - [ ] Simonson: Approximation Algorithms: https://www.youtube.com/watch?v=oDniZCmNmNw&list=PLFDnELG9dpVxQCxuD-9BSy2E7BWY3t5Sm&index=19
+    - Peter Norvik discusses solutions:
+        - http://nbviewer.jupyter.org/url/norvig.com/ipython/TSP.ipynb
 
 - [ ] **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