Find the First Palindrome

In this challenge, you will demonstrate your understanding of control flow in Rust. The task involves finding the first decimal palindrome in a given range.

What's a decimal palindrome?

A decimal palindrome is a number whose decimal (base 10, "normal") digits read the same backward as forward. This exercise will require you to find the numerically least non-negative palindrome in a given range. The easiest way to do this is to iterate through the range, check each number to see if it is a palindrome, and return the first palindrome found. You can use any control flow construct to solve this problem. (There are much more efficient ways to solve this problem, but the calculations get complex quickly.)

Palindromes are fascinating numbers, and finding them within a range will require clear control flow logic to ensure you identify the first one accurately.

Your task

You need to write a function, find_first_palindrome(start: i32, end: i32) -> Option<i32>, that takes two integer arguments start and end. The function should return the numerically least non-negative palindrome number within the range.

The range is inclusive: for example, if start == 1 and end == 1 the palindrome 1 is in range.
The range may have start > end, in which case it is still a valid range: for example, start == 3 and end == 1 contains the values 1, 2, 3.

If there are no palindromes in the range, the function should return None.

Requirements

The function should cover the numbers from start to end inclusive.
It should check each non-negative number to determine if it is a palindrome.
The function should return the numerically least palindrome found, or None if no palindromes exist in the range.
You must handle "reversed" ranges, when start is greater than end.

Example

let result = find_first_palindrome(10, 30);
assert_eq!(result, Some(11)); // 11 is the first palindrome in the range
 
let result = find_first_palindrome(100, 105);
assert_eq!(result, Some(101)); // 101 is the first palindrome in the range
 
let result = find_first_palindrome(123, 130);
assert_eq!(result, None); // No palindromes in this range
 
let result = find_first_palindrome(-130, -1);
assert_eq!(result, None); // No palindromes in this range
 
let result = find_first_palindrome(100, -105);
assert_eq!(result, Some(0)); // 0 is the first palindrome in the range

Did you know?

Did you know that palindromes are not just limited to numbers? They are found in words, phrases, and even DNA sequences! For example, the word "racecar" is a palindrome, as it reads the same backward and forward. Check out this "Weird Al" video for many many examples.

Palindromes are fascinating in various fields, including mathematics, literature, and biology, where they often have unique properties and significance.

Hints

To check if a number is a palindrome, you probably want to convert it to a String and compare it with its reverse.
You can get the chars in a String by using the chars() method on a String
You can iterate over values in reverse order by using the rev() method on an iterator. For example, you can get the chars in a String s in reverse order with s.chars().rev()
Use a loop, iterator, or any other control flow construct to check each number in the range until a palindrome is found or the range is exhausted.
Remember to handle the case where start is greater than end, probably by swapping the values if necessary.

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Solutions

Christopher Nielson

c-nielson

3 days ago

5.92ms

87.98kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    let mut my_start = start;
    let mut my_end = end;
    if start > end {
        my_start = end;
        my_end = start;
    }
    for num in my_start..=my_end {
        let num_str = num.to_string();
        if num_str == num_str.chars().rev().collect::<String>() {
            return Some(num);
        }
    }
    None
}

Muhammad-Dennis

7 days ago

3.43ms

87.98kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    // TODO: Implement the function here
    let (mut start, mut end) = (start, end);
    if start > end {
        let temp = start;
        start = end;
        end = temp;
    }
    for num in start..=end {
       let num_str = num.to_string();
       let reversed = num_str.chars().rev().collect::<String>();
       if num_str == reversed {
        return Some(num)
       }
    }
    None
}

エヴァンゲリオン

Lu-zihang

10 days ago

3.04ms

87.37kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    // TODO: Implement the function here
    let (st, en) = (start.min(end), end.max(start)) ;
    (st..=en).find(|&i| i.to_string().chars().rev().eq(i.to_string().chars()))
}

Sthitaprajna Sahu

sthitasahu

12 days ago

6.95ms

81.74kb

use std::cmp::{min,max};
pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    let s = min(start, end);
    let e = max(start, end);
    for i in s..=e{
        let mut num = i; 
        if is_palindrome(&mut num) {
            return Some(i);
        }
    }
    None
}
pub fn is_palindrome(num: &mut i32) -> bool {
    let original_number = *num; 
    let mut reversed_number = 0;
    while *num > 0 {
        let digit = *num % 10;
        reversed_number = reversed_number * 10 + digit;
        *num /= 10; 
    }
    original_number == reversed_number
}

Florian Gaudin-Delrieu

FlorianGD

12 days ago

4.51ms

87.37kb

use std::cmp::{min, max};
pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    // TODO: Implement the function here
    let s = min(start, end);
    let e = max(start, end);
    for i in s..=e {
        if is_palindrome(i.to_string()) {
            return Some(i)
        }
    }
    None
}
fn is_palindrome(s: String) -> bool {
    s.chars().zip(s.chars().rev()).all(|(c1, c2)| c1 == c2)
}

dawwestk

14 days ago

3.97ms

87.37kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    // TODO: Implement the function here
    let range = if start > end {
        end..=start
    } else {
        start..=end
    };
    'outer: for num in range {
        let s = num.to_string();
        let mut iter = s
            .chars()
            .zip(s.chars().rev());
        while let Some((a, b)) = iter.next() {
            if a != b {
                continue 'outer;
            } 
        }
        return Some(num)
    }
    None
}

Bart Massey

BartMassey

15 days ago

3.34ms

87.37kb

fn digits(mut value: i32) -> Vec<u8> {
    let d = std::iter::from_fn(|| {
        if value == 0 {
            None
        } else {
            let d = value % 10;
            value /= 10;
            Some(d as u8)
        }
    });
    d.collect()
}
fn is_palindrome(digits: &[u8]) -> bool {
    let ndigits = digits.len();
    for i in 0..(ndigits + 1) / 2 {
        if digits[i] != digits[ndigits - i - 1] {
            return false;
        }
    }
    true
}
pub fn find_first_palindrome(mut start: i32, mut end: i32) -> Option<i32> {
    if start > end {
        std::mem::swap(&mut start, &mut end);
    }
    (start..=end).find(|&i| {
        if i < 0 {
            return false;
        }
        let d = digits(i);
        is_palindrome(&d)
    })
 }

PangoSea

kapaseker

16 days ago

3.58ms

87.98kb

fn is_palindrome(n: i32) -> bool {
    let s = n.to_string();
    s == s.chars().rev().collect::<String>()
}
pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    if start <= end {
        for num in start..=end {
            if is_palindrome(num) {
                return Some(num);
            }
        }
    } else {
        for num in (end..=start) {
            if is_palindrome(num) {
                return Some(num);
            }
        }
    }
    None
}

Marco-Normal

17 days ago

3.79ms

87.37kb


pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    for num in start.min(end)..=end.max(start) {
        let num_ = num.to_string();
        if num_.chars().zip(num_.chars().rev()).all(|(c1, c2)| c1 == c2) {
            return Some(num)
        }
    }
    None
}

rawar089

18 days ago

3.19ms

87.98kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    // TODO: Implement the function here
    let mut s= start;
    let mut e = end;
    if e < s {
        (s, e) = (e, s);
    }
    for i in s..=e {
        if i < 0 { continue; }
        let p = i.to_string().chars().rev().collect::<String>().parse::<i32>().ok().unwrap();
        if p == i {
            return Some(i);
        }
    }
    None
}

vikingNR

19 days ago

6.46ms

87.98kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    // TODO: Implement the function here
    if end < start {
        for i in end..=start{
            let i_to_str = i.to_string();
            if i_to_str == i_to_str.chars().rev().collect::<String>(){
                return Some(i)
            }
        }
    }
    for i in start..=end{
        let i_to_str = i.to_string();
        if i_to_str == i_to_str.chars().rev().collect::<String>(){
            return Some(i)
        }
    }
    None
}

Algorab

20 days ago

4.78ms

87.38kb

pub fn find_first_palindrome(mut start: i32, mut end: i32) -> Option<i32> {
    if start > end {
        let tmp = start;
        start = end;
        end = tmp
    }
    for num in start..=end {
        if num.to_string().chars().rev().collect::<String>() == num.to_string() {
            return Some(num);
        }
    }
    None
}

Mikhail Shutov

mshutov

20 days ago

5.43ms

87.37kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    let from: i32;
    let to: i32;
    if start <= end {
        from = start;
        to = end;
    } else {
        from = end;
        to = start;
    }
    for candidate in from..=to {
        let rev: String = candidate.to_string().chars().rev().collect();
        if candidate.to_string() == rev {
            return Some(candidate);
        }
    }
    None
}

Joe Schneider

josschne

20 days ago

10.57ms

87.37kb

use std::cmp::{min, max};
pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    (min(start, end)..=max(start, end))
        .find(|&x| {
            let s = x.to_string();
            s.chars().eq(s.chars().rev())
        })
}

Ahmet Özcan

ahmetoozcan

21 days ago

4.35ms

87.37kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    // TODO: Implement the function here
    match start < end {
        true => (start..=end).find(|num| {
            let s = num.to_string();
            s.chars().eq(s.chars().rev())
        }),
        false => (end..=start).find(|num| {
            let s = num.to_string();
            s.chars().eq(s.chars().rev())
        }),
    }
}

Dominicm99

21 days ago

5.02ms

87.97kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    let mut a = start;
    let mut b = end;
    if start > end {
        b = start;
        a = end
    }
    for i in a..=b {
        if i.to_string().chars().eq(i.to_string().chars().rev()) {
            return Some(i);
        }
    }
    None
}

Balint Toth

tbali0524

22 days ago

3.28ms

81.74kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    // TODO: Implement the function here
    let mut from = start;
    let mut to = end;
    if start > end {
        from = end;
        to = start;
    }
    for num in from..=to {
        let mut n = num;
        let mut backward = 0;
        while n > 0 {
            let d = n % 10;
            n /= 10;
            backward = backward * 10 + d; 
        }
        if num == backward {
            return Some(num);
        }
    }
    None
}

nedrw

22 days ago

4.23ms

87.98kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    // TODO: Implement the function here
    let mut s = start;
    let mut e = end;
    if start > end {
        s = end;
        e = start;
    }
    for i in s..=e {
        let s = i.to_string();
        let rs: String = s.chars().rev().collect();
        if s == rs {
            return Some(i);
        }
    }
    None
}

zahrajavar

22 days ago

3.71ms

87.98kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    // TODO: Implement the function here
    let (start, end) = if start > end { (end, start) } else { (start, end) };
    let mut s = String::new();
    for num in start..end+1{
        s = num.to_string();
        if s == s.chars().rev().collect::<String>(){
            return Some(num);
        }
    }
    None
}

Lauri Sarap

LauriSarap

23 days ago

4.82ms

87.37kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    let (start, end) = if start > end { (end, start) } else { (start, end) };
    for number in start..=end {
        if number < 0 {
            continue;
        }
        if number < 10 {
            return Some(number);
        }
        let mut digits: Vec<i32> = vec![];
        let mut temp = number;
        while temp > 0 {
            digits.push(temp % 10);
            temp /= 10;
        }
        let digits_length = digits.len() as i32;
        let mut left: i32 = 0;
        let mut right: i32 = digits_length  - 1;
        let mut is_palindrome = true;
        while left < right {
            if digits[left as usize] == digits[right as usize] {
                left += 1;
                right -= 1;
            }
            else {
                is_palindrome = false;
                break;
            }
        }
        if is_palindrome {
            return Some(number);
        }
    }
    return None;
}

aey4

25 days ago

4.62ms

87.98kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    let (start, end) = (start.min(end), end.max(start)) ;
    for n in start..=end{
        if is_palindrome(n.to_string()){
            return Some(n);
    }
}
None
}
pub fn is_palindrome(string: String) -> bool {
    let string_reversed:String = string.chars().rev().collect();
    string == string_reversed
}

Benjamin Falk

lumio

25 days ago

3.63ms

87.97kb

use std::cmp;
pub fn is_palindrome(num: i32) -> bool {
    let different_count = num
        .to_string()
        .chars()
        .zip(num.to_string().chars().rev())
        .filter(|&(a, b)| a != b)
        .count();
    different_count == 0
}
pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    for i in cmp::min(start, end)..=cmp::max(start, end) {
        if is_palindrome(i) {
            return Some(i);
        }
    }
    None
}

aey4

25 days ago

3.37ms

87.37kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    // TODO: Implement the function here
    let (start, end) = (start.min(end), end.max(start)) ;
    for n in start..=end{
        if is_palindrome(n.to_string()){
            return Some(n);
    }
}
None
}
pub fn is_palindrome(string: String) -> bool {
     let mut reversed = string.clone();
     unsafe{
        let vec = reversed.as_mut_vec();
        vec.reverse();
     }
     string == reversed
}

aey4

25 days ago

5.30ms

87.97kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    // TODO: Implement the function here
    let (start, end) = (start.min(end), end.max(start)) ;
    for n in start..=end{
    let mut s = n.to_string();
    unsafe{
        let vec = s.as_mut_vec();
        vec.reverse();
    }
        if n.to_string() == s{
            return Some(n);
    }
}
None
}

aey4

a month ago

3.17ms

87.97kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    // TODO: Implement the function here
    let (s, e) = (start.min(end), end.max(start)) ;
    for n in s..=e{
    let mut s = n.to_string();
    unsafe{
        let vec = s.as_mut_vec();
        vec.reverse();
    }
        if n.to_string() == s{
            return Some(n);
    }
}
None
}

Yamami

Yamami1221

a month ago

3.43ms

87.98kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    let s: i32;
    let e: i32;
    if start > end {
        s = end;
        e = start;
    } else {
        s = start;
        e = end;
    }
    for i in s..=e {
        if is_palindrome(i.to_string()) {
            return Some(i);
        }
    }
    None
}
pub fn is_palindrome(string: String) -> bool {
    let rev = string.chars().rev().collect::<String>();
    return string == rev;
}

Caio César

caiocdcs

a month ago

3.52ms

87.37kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    let (st, en) = (start.min(end), end.max(start)) ;
    (st..=en).find(|&i| is_palindrome(i))
}
fn is_palindrome(n: i32) -> bool {
    let number = n.to_string();
    number.chars().zip(number.chars().rev()).all(|(l, r)| l == r)
}

RonaldoArayadev

a month ago

3.88ms

87.37kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    // TODO: Implement the function here
    let (st, en) = (start.min(end), end.max(start)) ;
    (st..=en).find(|&i| i.to_string().chars().rev().eq(i.to_string().chars()))
}

hubbardip

a month ago

3.12ms

87.37kb

fn digits(n: u32) -> Vec<u32> {
    let d = f32::log10(n as f32).floor() as u32 + 1;
    (1..=d).map(|k| (n / (10 as u32).pow(k - 1)) % 10).collect()
}
fn vec_is_palin<T: Clone + PartialEq>(v: Vec<T>) -> bool {
    let mut w = v.clone();
    w.reverse();
    v.iter().zip(w.iter()).all(|(a, b)| a == b)
}
pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    if start > end {
        return find_first_palindrome(end, start);
    }
    for i in start..=end {
        if i < 0 {
            continue;
        }
        if vec_is_palin(digits(i.abs() as u32)) {
            return Some(i);
        }
    }
    None
}

vgpetrov

a month ago

4.94ms

87.37kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    let mut inclusive = start..=end;
    if start > end {
        inclusive = end..=start;
    }
    for i in inclusive {
        let i_string = i.to_string();
        let mut found = true;
        for (a, b) in i_string.chars().zip(i_string.chars().rev()) {
            if a != b {
                found = false;
                break;
            }
        }
        if found {
            return Some(i);
        }
    }
    None
}

viky

vikyw89

a month ago

3.74ms

87.37kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    // TODO: Implement the function here
    // handle start bigger than end
    let new_start = start.min(end);
    let new_end = end.max(start);
    for i in new_start..=new_end {
        if is_number_palindrome(i) {
            return Some(i);
        }
    }
    return None;
}
fn is_number_palindrome(n: i32) -> bool {
    // 2 pointers
    let mut start = 0;
    let mut end = n.to_string().len() - 1;
    while start < end {
        if n.to_string().chars().nth(start) != n.to_string().chars().nth(end) {
            return false;
        }
        start += 1;
        end -= 1;
    }
    return true;
}

jon-a-miller

a month ago

3.50ms

87.37kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    let (st, en) = (start.min(end), end.max(start)) ;
    (st..=en).find(|&i| i.to_string().chars().rev().eq(i.to_string().chars()))
}

JeppeFoldberg

a month ago

4.74ms

87.98kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    for number in start.min(end)..=start.max(end) {
        let number_string = number.to_string();
        let number_string_reversed = number_string.chars().rev().collect::<String>();
        if number_string == number_string_reversed {
            return Some(number)
        }
    }
    None
}

Denis SOURON

Brack0

a month ago

3.57ms

87.37kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    let mut range = if end >= start {
        start..=end
    } else {
        end..=start
    };
    range.find(|&x| {
        let x_string = x.to_string();
        x_string.chars().eq(x_string.chars().rev())
    })
}

Giuliano

GiulianoCTRL

a month ago

3.42ms

81.74kb

// A bit overkill, but I felt like traits...
pub trait Reverse {
    fn reverse(&self) -> Self;
}
pub trait Palindrome: Reverse + Sized
where
    Self: PartialEq<Self>,
{
    fn is_palindrome(self) -> bool {
        self == self.reverse()
    }
}
impl Reverse for i32 {
    fn reverse(&self) -> Self {
        let mut n = *self;
        let radix = 10;
        let mut reversed = 0;
        while n > 0 {
            reversed = reversed * radix + n % radix;
            n /= radix;
        }
        reversed
    }
}
impl Palindrome for i32 {}
pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    (start.min(end)..=start.max(end))
        .find(|&i| i.is_palindrome())
}

Chris

chriswmann

a month ago

3.27ms

81.74kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    (start.min(end)..=start.max(end))
        .filter_map(|number| (number == reverse_num(number))
        .then_some(number))
        .next()
}
fn reverse_num(mut number: i32) -> i32 {
    let mut reversed = 0;
    while number > 0 {
        reversed *= 10;
        reversed += number % 10;
        number /= 10;
    }
    reversed
}

Chris

chriswmann

a month ago

3.35ms

81.74kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    (start.min(end)..=start.max(end))
        .filter_map(|number| (number == reverse_num(number))
        .then_some(number))
        .next()
}
fn reverse_num(mut number: i32) -> i32 {
    let mut reversed = 0;
    while number > 0 {
        reversed *= 10;
        reversed += number % 10;
        number /= 10;
    }
    reversed
}

Chris

chriswmann

a month ago

3.20ms

87.98kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    // TODO: Implement the function here
    for n in (start.min(end)..=end.max(start)).into_iter() {
        let m = n.to_string();
        if is_palindrome(m) {
            return Some(n);
        }
    }
    None
}
fn is_palindrome(s: String) -> bool {
    s == s.chars().rev().collect::<String>()
}

Chris

chriswmann

a month ago

3.57ms

87.98kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    // TODO: Implement the function here
    let s = std::cmp::min(start, end);
    let e = std::cmp::max(start, end);
    for n in (s..=e).into_iter() {
        let m = n.to_string();
        if m == m.chars().rev().collect::<String>() {
            return Some(n);
        }
    }
    None
}

Võ Thanh Bình

pynhpo

a month ago

3.00ms

87.99kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    for num in start.min(end)..=(end.max(start)) {
        let num_as_string = num.to_string();
        let num_chars: Vec<char> = num_as_string.chars().collect();
        let num_len = num_chars.len();
        for (i, &c) in num_chars.iter().enumerate() {
            if num_len == 1 || i > (((num_len - 1) / 2) as usize) {
                return Some(num);
            }
            if c != num_chars[num_len - 1 - i] {
                break;
            }
        }
    }
    None
}

Dagur Arinbjörn Daníelsson

gardyna

a month ago

3.22ms

87.38kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    for i in start.min(end)..=(end.max(start)) {
        let a = i.to_string();
        let b: String = i.to_string().chars().rev().collect();
        if a == b {
            return Some(i)
        }
    }
    None
}

mgreve

a month ago

4.09ms

87.37kb

fn is_palindrome(n: i32) -> bool {
    let s = n.to_string();
    let count = s.chars().count();
    for i in 0..count/2 {
        if s.chars().nth(i) != s.chars().nth(count-1-i) {
            return false;
        }
    }
    true
}
pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    for n in core::cmp::min(start, end)..=core::cmp::max(start, end) {
        if is_palindrome(n) {
            return Some(n);
        }
    }
    None
}

Shoma Kobayashi

kobapi28

a month ago

3.10ms

87.98kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    let mut min = start;
    let mut max = end;
    if min > max {
        let tmp = min;
        min = max;
        max = tmp;
    }
    for n in min..=max {
        let stri: String = n.to_string();
        let reversed = stri.chars().rev().collect::<String>();
        if stri == reversed {
            return Some(n);
        }
    }
    None
}

Javier Garcia

javigar322

a month ago

3.27ms

87.37kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    // TODO: Implement the function here
    let mut i = start;
    let mut j = end;
    if i > j {
        j = j + i;
        i = j - i;
        j = j - i;
    }
    while i <= j {
        let num:String = i.to_string();
        let mut left = 0;
        let mut right = num.len()-1;
        let mut ans = true;
        while left<right {
            if num.chars().nth(left) != num.chars().nth(right) {
                ans = false;
                break;
            }
            left+=1;
            right-=1;
        }
        if ans {
            return Some(i);
        }
        i+=1;
    }
    None
}

martin-unit

a month ago

3.32ms

87.37kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    // TODO: Implement the function here
    let mut i = start;
    let mut j = end;
    if i > j {
        j = j + i;
        i = j - i;
        j = j - i;
    }
    while i <= j {
        let num:String = i.to_string();
        let mut left = 0;
        let mut right = num.len()-1;
        let mut ans = true;
        while left<right {
            if num.chars().nth(left) != num.chars().nth(right) {
                ans = false;
                break;
            }
            left+=1;
            right-=1;
        }
        if ans {
            return Some(i);
        }
        i+=1;
    }
    None
}

Esteban Soba

XtebanUy

a month ago

4.19ms

87.37kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    // TODO: Implement the function here
    let (fstart, fend) = if start < end {(start,end)} else {(end,start)};
    'outer: for number in fstart..=fend {
        let number_str = number.to_string();
        for (char, revchar)  in number_str.chars().zip(number_str.chars().rev())
        {
            if char != revchar {
                continue 'outer;
            }
        }
        
        return Some(number);
    }
    None
}

Len Remmerswaal

LenRemmerswaal

a month ago

3.20ms

87.42kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    println!("{start}..{end}");
    if start <= end {
        (start..=end).find(|n| is_palindrome(*n))
    } else {
        (end..=start).find(|n| is_palindrome(*n))
    }    
}
fn is_palindrome(num: i32) -> bool {
    let numstr: Vec<_> = num.to_string().chars().collect();
    let mut pos = 0;
    let end = numstr.len() - 1;
    while pos < end - pos {
        if numstr[pos] != numstr[end - pos] {
            return false;
        }
        pos += 1;
    }
    true
}

Len Remmerswaal

LenRemmerswaal

a month ago

3.40ms

87.42kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    println!("{start}..{end}");
    if start <= end {
        (start..=end).find(|n| is_palindrome(*n))
    } else {
        (end..=start).find(|n| is_palindrome(*n))
    }    
}
fn is_palindrome(num: i32) -> bool {
    let numstr: Vec<_> = num.to_string().chars().collect();
    let mut pos = 0;
    let end = numstr.len() - 1;
    while pos < end {
        if numstr[pos] != numstr[end - pos] {
            return false;
        }
        pos += 1;
    }
    true
}

Dan Callaghan

danc86

a month ago

3.37ms

87.38kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    let (start, end) = if start <= end { (start, end) } else { (end, start) };
    for n in start..=end {
        if n.to_string().chars().rev().collect::<String>() == n.to_string() {
            return Some(n);
        }
    }
    None
}

r1kk1s

a month ago

3.35ms

87.98kb

pub fn find_first_palindrome(start: i32, end: i32) -> Option<i32> {
    let mut s = start;
    let mut e = end;
    if s > e {
        e = start;
        s = end;
    };
    for num in s..=e {
        let num_string = num.to_string();
        if num_string == num_string.chars().rev().collect::<String>() {
            return Some(num);
        }
    }
    println!("{start}{end}");
    None
}