Count the palindromic substrings

def count_palindromes(s):
    total = 0
    for centre in range(2 * len(s) - 1):          # characters and gaps
        lo, hi = centre // 2, (centre + 1) // 2
        while lo >= 0 and hi < len(s) and s[lo] == s[hi]:
            total += 1                            # s[lo..hi] is a palindrome
            lo -= 1
            hi += 1
    return total

#include <string>

int solve(std::string s) {
    int n = s.size(), total = 0;
    for (int c = 0; c < 2 * n - 1; ++c)
        for (int lo = c / 2, hi = (c + 1) / 2; lo >= 0 && hi < n && s[lo] == s[hi]; --lo, ++hi) ++total;
    return total;
}

class Solution {
    public int countPalindromes(String s) {
        int n = s.length(), total = 0;
        for (int c = 0; c < 2 * n - 1; c++)
            for (int lo = c / 2, hi = (c + 1) / 2; lo >= 0 && hi < n && s.charAt(lo) == s.charAt(hi); lo--, hi++) total++;
        return total;
    }
}

function countPalindromes(s) {
  let total = 0;
  for (let c = 0; c < 2 * s.length - 1; c++)
    for (let lo = c >> 1, hi = (c + 1) >> 1; lo >= 0 && hi < s.length && s[lo] === s[hi]; lo--, hi++) total++;
  return total;
}

fn solve(s: &str) -> i64 {
    let c: Vec<u8> = s.bytes().collect();
    let n = c.len() as i64;
    let mut total = 0;
    for centre in 0..2 * n - 1 {
        let (mut lo, mut hi) = (centre / 2, (centre + 1) / 2);
        while lo >= 0 && hi < n && c[lo as usize] == c[hi as usize] {
            total += 1;
            lo -= 1;
            hi += 1;
        }
    }
    total
}

import Data.Array

solve :: String -> Int
solve s = sum [expand (c `div` 2) ((c + 1) `div` 2) | c <- [0 .. 2 * n - 2]]
  where
    n = length s
    a = listArray (0, n - 1) s
    -- the number of palindromes around one centre
    expand lo hi
      | lo >= 0 && hi < n && a ! lo == a ! hi = 1 + expand (lo - 1) (hi + 1)
      | otherwise = 0