Modification and New Addition of Links (EbookFoundation#2016)

* Modification and New Addition of Links

Modified some links to reach the specific page and added some more links
to programming contest and problem set.

* Corrected sequence of links

* Ruby Interactive Tutorial Added

Author: akritithakur

free-programming-interactive-tutorials-en.md

@@ -186,6 +186,7 @@
 
 * [CodeCademy Ruby](https://www.codecademy.com/learn/ruby)
 * [Codeschool Ruby paths](https://www.codeschool.com/paths/ruby)
+* [Hackety Hack](http://www.hackety.com)
 * [Ruby Koans](http://www.rubykoans.com)
 * [RubyMonk - Interactive Ruby tutorials](https://rubymonk.com)
 * [The Odin Project](http://www.theodinproject.com)

problem-sets-competitive-programming.md

@@ -8,11 +8,12 @@
 ### Competitive Programming
 
 * [4Clojure](http://www.4clojure.com)
+* [A2 Online Judge](https://a2oj.com)
 * [Codeabbey](http://www.codeabbey.com)
 * [Codechef](https://www.codechef.com/contests)
 * [Codeeval](https://www.codeeval.com)
 * [CodeFights](https://codefights.com)
-* [Codeforces](http://codeforces.com)
+* [Codeforces](http://codeforces.com/contests)
 * [Coderbyte](https://coderbyte.com)
 * [Codewars](http://www.codewars.com)
 * [Codingame](https://www.codingame.com/start)
@@ -23,6 +24,7 @@
 * [Just another Golf Coding](http://jagc.org)
 * [Microcorruption](https://microcorruption.com/login)
 * [Saratov State University](http://acm.sgu.ru/index.php)
+* [Sphere Online Judge](http://www.spoj.com/contests)
 * [Topcoder](https://www.topcoder.com)
 
 
@@ -33,10 +35,12 @@
 
 ### Problem Sets
 
+* [A2 Online Judge](https://a2oj.com/ps)
 * [Advent Of Code](http://adventofcode.com)
 * [Anarchy Golf](http://golf.shinh.org)
 * [CareerCup](http://www.careercup.com)
 * [CheckIO](http://www.checkio.org)
+* [Codeforces](https://www.codeforces.com/problemset)
 * [CodeHunt](https://www.codehunt.com)
 * [Codility](https://codility.com/programmers/)
 * [Coding Bat](http://codingbat.com/java)
@@ -55,7 +59,7 @@
 * [Project Euler](https://projecteuler.net)
 * [Python Practice Projects](http://pythonpracticeprojects.com)
 * [Rosalind](http://rosalind.info/problems/locations/)
-* [Sphere Online Judge](http://www.spoj.com)
+* [Sphere Online Judge](http://www.spoj.com/problems/classical)
 * [TalentBuddy](http://www.talentbuddy.co/blog/)
 * [Timus Online Judge](http://acm.timus.ru)
 * [URI Online Judge](https://www.urionlinejudge.com.br/judge/login)