This english don't understanding. anything explain to me this sentence.

[kns5498]

Hi, I’m a korean. I’m not good yet English. So, I don’t understand a sentence.

This mapping is one-to-one and onto, which means that the same input letter always gets replaced with the same output letter, and different input letters always get replaced with different output letters.

This sentence is A.Problem in google code jem Qualification Round 2012.
https://code.google.com/codejam/contest/1460488/dashboard

I understand “one-to-one”, it same “1:1”.

but, “onto” don’t understand to mean.

in English-Korean dictionary, To mean “onto” is same “across”.
ex) When my name was called, he looked across at me.

but, It isn’t right mean. So, I asked help you.

And, I find To mean “onto”, Do “onto” same The link?

Surjective function

please~

[ReBirth]

The one-to-one seems to be relationship, not just value comparison. One input letter is only owing one output letter.

[SHC]

we take any message and replace each English letter with another English letter. This mapping is one-to-one and onto, which means that the same input letter always gets replaced with the same output letter, and different input letters always get replaced with different output letters. A letter may be replaced by itself. Spaces are left as-is.

They are replacing characters in a string (say sentence). A character is always replaced by another character.