How to stop allowing offbyone error?

Question

Algorithms

How to stop allowing offbyone error? When implementing algorithms, sometimes I make mistakes. Maybe there are some rules? Secret Chinese techniques and tricks?

Answer 1

These errors are, in fact, logical ones.
So, in order to prevent them, you need to follow the logic and meaning. The main tools that can help with this are decomposition into small fragments and meaningful naming of variables and functions. It's easy to make a mistake if you have, for example, three identical nested loops with variables i , j and k .

Answer 2

Olympiad programming helped me.
It quickly becomes obvious that it is more profitable to write without error right away than to painfully look for it later.
In general, I had to force myself to be more careful with these indexes. And over time it got easier.
But in general, the best way to avoid offbyone errors is to not use indexes at all.
There are all sorts of twists. For each instead of for and so on. And in general, more standard algorithms/functions.
Here's an example for C++: Let's say you need to take the last element of an array of length n. Then the index of this element will be equal to n-1. Here is your chance to be wrong. But if you use a vector instead of an array, then you can simply take back() from it.