C 几次读入后程序变慢

Question

So i have to write a C program for class, that solves a connect four like game, that roughly said resolves matches of same colored pieces, lets pieces above fall down, then checks again for matches, if no matches were found it drops the next piece and so on.

My given input is a text file, where each line holds information about the color and the x-position, where the piece is supposed to fall down. My implementation is based on AVL-trees and my program works fine for inputs roughly up to 2.000.000 lines and solves it in about 3 seconds. One bigger example file i have to solve is roughtly 2.600.000 lines long but doesnt terminate. The program reads in about 1.000.000 lines per second but right after about the 2.000.000 mark its slows down tremendously and only reads in a couple 100 lines per second.

Its one of my first "bigger" projects and has about 900 lines of code, so i dont see the point in posting it here (unless someone really wants to see it)

I am really clueless what the cause could be, so maybe someone of you has an idea or can point me in a direction for things i have to look out for.

Answer 1

Add logging with timestamps to spot where the slowdown occurs. You need to isolate the code that has the performance issue.

The first step to getting better is to measure where you currently are. Once you know how long the current process takes, you can decide if a change you make helps, hurts or makes no change.

There's a vast world of software optimization, look around for expensive loops. Read up on big oh notation. If you have a loop that processes a loop that processes a loop O(n^3), what seems fast with 100 iterations each can slow down dramatically when each loop is a million.

If you have a performance profiler it can help organize the timestamps from the logs it creates so that the code that's taking the most time is highlighted. Many times what happens in cases like this is that something that seems good enough when you start out isn't good enough once you start to scale.

Nobody says you have to add log to every single line of your source code. That can be overwhelming. Figuring out what you don't have to focus on can be very helpful.