Competitive Programming: Two Simple Tricks in C++ To Make Code Faster

Competitive programmers ALWAYS use these two lines of code. Here’s why:

C++ has two functions:

• “cin” – Stands for character input. Reads an input from the standard IO.
• “cout” – Outputs text (like printing to a terminal).

By default, these are synchronized with C’s “scanf” and “printf” functions. When we use “cout” to print something, our C++ layer communicates with the C stdio layer to keep them in sync. This is slow.

In competitive programming, we don’t care about this synchronization. That’s where the first line “ios::sync_with_stdio(false)” comes from. It decouples the two layers. This makes our code significantly faster, especially in IO heavy questions.

When we use “cout” it doesn’t print the output immediately. That requires communicating with the operating system which is slow. Instead, our output gets pushed to a buffer which is eventually flushed.

By default “cin” is tied to “cout”. Before every “cin” read, the “cout” buffer is automatically flushed. In normal programs this helps keep the IO correct but again isn’t needed in competitive programming. So “cin.tie(nullptr)” removes that tie.

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
}

When I was in high school, I participated in NOIP, and at that time we used Turbo Pascal. In programming contests, readability wasn’t a priority. We often used all kinds of clever or tricky techniques, and the resulting code was hard to understand—but that didn’t stop us from winning awards.

Competitive programming emphasizes efficiency and ingenuity rather than maintainability. There’s even an annual C Obfuscation Contest where the submitted code is almost impossible to read, yet still runs correctly and produces impressive results.

Similarly, many Python solutions can be written in just one or two lines and look “magical,” but in real industrial settings they are often impractical to maintain or extend.

Contest code and production code are fundamentally two very different mindsets.

–EOF (The Ultimate Computing & Technology Blog) —