Add Elementary Algorithms book

free-programming-books.md

@@ -247,6 +247,7 @@
 * [Data Structures and Algorithms: Annotated Reference with Examples](https://drive.google.com/file/d/0B48k2jhdQ5P2aVlmMFB1UUJLczA/edit?usp=sharing)
 * [Data Structures Succinctly Part 1, Syncfusion](http://www.syncfusion.com/resources/techportal/ebooks/datastructurespart1) (PDF, Kindle) *(Just fill the fields with any values)*
 * [Data Structures Succinctly Part 2, Syncfusion](http://www.syncfusion.com/resources/techportal/ebooks/datastructurespart2) (PDF, Kindle) *(Just fill the fields with any values)*
+* [Elementary Algorithms](https://github.com/liuxinyu95/AlgoXY) - Larry LIU Xinyu
 * [Foundations of Computer Science](http://infolab.stanford.edu/~ullman/focs.html) - Al Aho and Jeff Ullman
 * [Open Data Structures: An Introduction](http://www.aupress.ca/index.php/books/120226) - Pat Morin
 * [LEDA: A Platform for Combinatorial and Geometric Computing](http://www.mpi-inf.mpg.de/~mehlhorn/LEDAbook.html)