Websites: Add Princeton University on algorithms and Java

websites/README.md

@@ -172,11 +172,12 @@ The Open University."_
 ### Algorithms
 
 - [Algorithms in the "Real World" (2018)](http://www.cs.cmu.edu/~guyb/realworld.html) - Compression, error correcting codes, cryptography, parallel algorithms, locality and I/O efficient algorithms, indexing and searching, nearest neighbors, dimensionality reduction.
+- [Algorithms, 4th Edition](https://algs4.cs.princeton.edu/home/) - Princeton University - _"Essential information that every serious programmer needs to know about algorithms and data structures."_
 - [Comparison of Algorithms](https://en.wikipedia.org/wiki/Sorting_algorithm#Comparison_of_algorithms) - See time complexity at a glance for various popular algorithms.
 - [Dictionary of Algorithms and Data Structures](https://xlinux.nist.gov/dads) - _"This is a dictionary of algorithms, algorithmic techniques, data structures, archetypal problems, and related definitions."_
 - [Introduction to algorithms](https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-006-introduction-to-algorithms-fall-2011/) ([problem sets](https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-006-introduction-to-algorithms-fall-2011/assignments/)) - MIT OpenCourseWare.
 - [Khan Academy - Algorithms](https://www.khanacademy.org/computing/computer-science/algorithms/) - _"We've partnered with Dartmouth college professors Tom Cormen and Devin Balkcom to teach introductory computer science algorithms, including searching, sorting, recursion, and graph theory. Learn with a combination of articles, visualizations, quizzes, and coding challenges."_
-- [Skiena's Algorithms Lectures](https://www3.cs.stonybrook.edu/~algorith/video-lectures/)
+- [Skiena's Algorithms Lectures](https://www3.cs.stonybrook.edu/~algorith/video-lectures/).
 
 #### Visualizations
 
@@ -509,6 +510,7 @@ _"Disposable email addressing, also known as DEA or dark mail, refers to an appr
 
 ### Java
 
+- [Introduction to Programming in Java](https://introcs.cs.princeton.edu/java/home/) - Princeton University - _"Textbooks for a first course in computer science for the next generation of scientists and engineers."_
 - [JetBrains Academy](https://www.jetbrains.com/academy) - _"You’ll progress through the track building around 5 different projects. Eventually you’ll be able to create a project that will showcase your skills at the junior Java Developer level."_.
 
 ### JavaScript