So, presumably you're here because you're stuck on a problem; your code seems to be working perfectly on your computer but the judge is consistently telling you you've got something wrong, and you're here looking for help. Welcome to the forums; hopefully you'll find exactly what you're looking for here
I'm sure you're in a hurry to get some help, but first.. here's a few tips to help you along your way.
Check your input/output methods. In C++, using cin and cout is too slow. Use these, and you will guarantee not being able to solve any problem with a decent amount of input or output. Use printf and scanf instead. In java, a Scanner is even worse. Using a BufferedReader is your best bet for most problems. If you code in other languages, check the specific language forum to see if you can find any pointers there.
Test your code on boundary cases. In particular, make sure your code runs on the largest possible input - often this will show you your algorithm is too slow, or your variables are overflowing. Testing on the smallest possible input, a 'zero'-type input, or anything else that may be a special case, will be a great help.
Search! There are many many hints + test cases in this forum and it is quite possible the hint you need has already been posted. Enter in the name or problem code in the search box at the top right of your screen and see if that helps.
If all three of these methods are fruitless, feel free to make a post. Make sure you include the problem code (the code you see in the URL) in the subject so people can easily find the problem you are talking about, and/or a link to the problem itself. This will also help people searching for the same problem later. Paste your code into code tags so it will be readable. And finally, let us know what your code does and what you've tried to do to fix it - if all you post is a long complicated algorithm with no other details it's going to be hard for anyone to understand what you've done right, let alone done wrong.
Code preformatting look like this...
It preserve's indentation.
To do code formatting, paste your code in. Then select it all, and click on the "Preformatted text button"
Last of all, if you've posted code which is very close to accepted, it's probably a good idea to edit your post to remove the code once you've fixed it so people who haven't solved the problem can't simply copy your code in the future.
Good luck with your problem solving