OJ Board

I'm not an experienced programmer myself. So it maybe a stupid question. But often wonder that how the highest rank holders in most problems in uva solve them in 0 ms.
Even when I submitted a code by just writing: I took 13ms. So how do they solve these problems so efficiently. do they use any library or algorithm? And what do I need to learn to solve problems efficiently like them..?

You can submit the same code twice in a row and get slightly different runtimes. It depends on many factors outside your control. Perhaps the old server gave faster runtimes.