how to reduce time limit exceed?

when i submit a problem sometimes it shows time limit exceeds .
so how can i reduce my time limit and how can i make it efficient

Use efficient algorithms (depending on the constraints).Or if there are large I/O files in the program use fast I/O methods.For more idea about faster I/O methods refer the problem INTEST :

link-http://www.codechef.com/problems/INTEST

Hope that this helps :).

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