Good Web Sites to train your algorithmic skills:
http://www.leetcode.com/
http://www.careercup.com
http://www.topcoder.com
http://codeforces.com
http://www.spoj.com
http://uva.onlinejudge.org
http://projecteuler.net
http://www.usaco.org
http://prepare.hackerearth.com
Site for collaborative coding:
http://collabedit.com
Source Code of the most popular data structures and algorithms in JAVA
http://code.google.com/p/java-algorithms-implementation/
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