Segment Tree I learned from this. The code is simple if u do reverse engg.

You can practice on Codeforces, LightOJ...

For example, you can try to solve http://codeforces.me/problemset/problem/381/E

thanks for your ideas.

Here are some helpful posts:

• http://codeforces.me/blog/entry/3327
• http://www.topcoder.com/tc?d1=tutorials&d2=lowestCommonAncestor&module=Static
• http://www.geeksforgeeks.org/segment-tree-set-1-sum-of-given-range/
• http://www.geeksforgeeks.org/segment-tree-set-1-range-minimum-query/

These posts describe lazy propagation, a very useful technique:

• http://isharemylearning.blogspot.gr/2012/08/lazy-propagation-in-segment-tree.html
• http://se7so.blogspot.gr/2012/12/segment-trees-and-lazy-propagation.html