Hello,
As I said in the previous post that I have started learning Rust and made a simple fibonacci series generator. Today I made a palindrome string checker. it’s very basic. I haven’t used Enum or Struct in the code since I don’t think it’s necessary in this simple code.
here is the code:
use std::io;
fn main() {
let mut input = String::new();
let stdin = io::stdin();
stdin.read_line(&mut input).unwrap(); // we want to exit in case it couldn't read from stdin
input = input.replace("\n", ""); // Removing newline
let mut is_palindrome: bool = true;
for i in 0..input.len()/2 {
let first_char: &str = &input[i..i+1];
let last_char: &str = &input[input.len()-i-1..input.len()-i];
if first_char != "\n" {
if first_char != last_char {
is_palindrome = false;
}
}
}
println!("palindrome: {}", is_palindrome);
}
There is a much nicer way of checking.
Rust iterators are really powerful. Try using them instead of loops, whenever you can.
Tap for solution
let is_palindrome = input.chars().eq(input.chars().rev());As you can see, the intent is much clearer instead of indexing into the loops. Technically this does however twice as many comparisons. They can be avoided with take and half the size of the iterator.
let is_palindrome = input.chars().eq(input.chars().rev());
wow, this is really awesome. you just made a single liner for this whole problem. I didn’t know that you could do something like this since I don’t know much about Rust yet.
There’s so many useful methods for iterators its worth reading the doc page to familiarize yourself. Its wicked powerful: https://doc.rust-lang.org/std/iter/trait.Iterator.html
You only need to check half of the string, so I think a technically optimal solution would have some take_while and maybe char_indices in there…
That’s exactly what I Hinted at in my post, though I would use take(input.size()/2). However I wouldn’t be surprised if the compiler could short circuit it, but I haven’t checked.
Oh yeah I can’t read 😄
I would be extremely surprised if any compiler was smart enough to short circuit that.
I would be a little less surprised if checking the whole string was actually faster anyway though… but I would still bet against it.
I didn’t see it mentioned but you could remove all trailing & leading whitespace with:
input = input.trim();Instead of using replace.
Such posts are more suitable as microblogs IMHO.
Anyway, string lengths are byte lengths, and indexing strings is actually not panic-safe. This is why we have (still-nightly) char-boundary methods now.
If you want to work on characters. use
.chars().count()and.chars().nth().And character boundaries are themselves not always grapheme boundaries, which is also something that you might need to keep in mind when you start writing serious code.
With all that in mind, you should realize, for example, that probably every string reversing beginner exercise answer in every language is actually wrong. And the wrongness may actually start at the underspecified requirements 😉
Aside from the better solution with iterators that Flipper mentioned, you can also:
- Omit the type annotation for
is_palindrome- it will be inferred asboolanyway break;after settingis_palindrome = false- Use the
(0..input.len()/2).all(|i| ...)iterator method instead.
Thank you for the suggestion, I will keep these in mind.
- Omit the type annotation for
Once palindrome is false, might as well break.
In what scenario could the first character be a newline character? I think that if-statement may be unnecessary, but I never use raw user input like you are here.
If the user only presses Enter then the first character would be “\n”.
I’m not sure that you need a range when pulling the character from the
inputvariable. Simplyinput[i]andinput[input.len() - i - 1]should work.yeah, you are right. Thanks for pointing out.
