Merge pull request #259 from JNajera/master

Fundamental Algorithms book & Ruby tutorial (ES)

free-programming-books-es.md

@@ -43,6 +43,7 @@
 
 ###Ruby
 
+* [Ruby en 20 minutos](https://www.ruby-lang.org/es/documentation/quickstart/)
 * [Guía para aprender a programar con Ruby. Adaptación al español del libro "Learn to Program" de Chris Pine](https://github.com/rubyperu/aprende.a.programar)
 * [Ruby en 20 minutos](https://www.ruby-lang.org/es/documentation/quickstart/)
 

free-programming-books.md

@@ -151,6 +151,7 @@
 * [Algorithms and Data-Structures](http://www.ethoberon.ethz.ch/WirthPubl/AD.pdf) (PDF)
 * [Algorithms](http://www.cs.berkeley.edu/~vazirani/algorithms.html) (draft)
 * [Algorithms Course Materials](http://compgeom.cs.uiuc.edu/~jeffe/teaching/algorithms/) - Jeff Erickson
+* [Algorithms, 4th Edition](http://algs4.cs.princeton.edu/home/) - Robert Sedgewick and Kevin Wayne
 * [Binary Trees](http://cslibrary.stanford.edu/110/BinaryTrees.pdf) (PDF)
 * [Clever Algorithms](http://www.cleveralgorithms.com/nature-inspired/index.html)
 * [Computational Geometry: Algorithms and Applications](http://www.cs.uu.nl/geobook/) (chapters 1 and 9, pseudo-code)