 Jaewoo Song

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During these several days, I have suffered from runtime errors while solving Baekjoon Online Judge problems.

Of course, I managed to solve them but I think it is useful to wrap up the reasons why I got runtime errors this time.

These are general cases that cause a runtime error.

• The code refers to the spot out of the range of given arrays.

• The size of a global array exceeds the size of the memory’s data section.

• The size of a local array exceeds the size of the stack.

• A number is divided by $0$.

• The library itself triggers an exception.

• Recursive calls become too deep.

• The code refers to the already released memory section.

• The main function returns a number which is not $0$.

(Reference: https://www.acmicpc.net/board/view/22980)

I made two mistakes.

One case is that I misunderstood the problem so I declared the size of a vector smaller than that of the problem’s condition and the spot which is located out of the array was referred to.

And another case is that when I built a customized comparing function to use sort, I used <= and >=, not < or >.

The former is one of the cases I mentioned, so I will skip it.

Let’s focus on the latter.

https://en.wikipedia.org/wiki/Weak_ordering

This is the reference about the above error and honestly, I have no idea what this document is saying. For a simpler version, this is what I understood.

When sorting the values, the standard usually has a condition like this: As $a<b$, therefore “a” should come before “b”.

In other words, the statement that if $a<b$, this must not be $b<=a$ should be guaranteed to implement a proper sorting mechanism

. If one wants to include the “same” case and puts a sign of equality to inequality signs, the compiler understands the code like this: Both $a<b$ and $b<a$ are correct.

This is obviously a contradiction, so it triggers a runtime error.

Actually, I have seen that information somewhere but I just didn’t care about it that much.

Honestly, I didn’t expect to be blocked by this principle in problem-solving.

I’m learning a lot every day…