>>234
Rust

fn foo(n: usize) -> (usize, Option<usize>) {
　let n2b = |n: usize| { let mut o = Some(n); iter::from_fn(|| { let n = o.take()?; o = (n >= 10).then(|| n / 10); Some((n % 10) as i8) }).collect::<Vec<i8>>() };
　let b2n = |b: &[i8]| b.iter().rev().fold(0_usize, |n, b| n * 10 + *b as usize);
　let pal = |b: &mut [i8]| { let len = b.len() / 2; let (l, u) = b.split_at_mut(len); iter::zip(l, u.iter().rev()).for_each(|(l, u)| *l = *u); };
　let inc = |b: &mut [i8]| { let len = b.len() / 2; let mut c = 1; b[len..].iter_mut().for_each(|b| { *b += c; if *b > 9 { *b = 0; c = 1; } else { c = 0; }}); };
　let dec = |b: &mut [i8]| { let len = b.len() / 2; let mut c = 1; b[len..].iter_mut().for_each(|b| { *b -= c; if *b < 0 { *b = 9; c = 1; } else { c = 0; }}); };
　let fix = |b: &mut [i8]| { if b.last() == Some(&0) { if b.len() & 1 == 0 { b[(b.len() - 1) / 2] = 9; } true } else { false } };
　
　let mut b = n2b(n);
　pal(&mut b);
　let n1 = b2n(&b);
　match n.cmp(&n1) {
　　Ordering::Equal => return (n, None),
　　Ordering::Greater => inc(&mut b),
　　Ordering::Less => dec(&mut b),
　}
　if fix(&mut b) { b.pop(); }
　pal(&mut b);
　let n2 = b2n(&b);
　match n.abs_diff(n1).cmp(&n.abs_diff(n2)) {
　　Ordering::Less => (n1, None),
　　Ordering::Greater => (n2, None),
　　Ordering::Equal => (n1, Some(n2)),
　}
}