Given a string s, return the longest palindromic substring in s. O(n^2) brute force solution. This is a very slow solution instead use dynamic programming and constructed intersection tables. Here are examples of how to do it optimally https://leetcode.com/problems/longest-palindromic-substring/solutions/127837/longest-palindromic-substring/

Longest-Palindromic-Substring.rs

use std::collections::HashMap;

pub fn longest_palindrome(s: String) -> String {
    let mut poly: HashMap<String, usize> = Default::default();
    for i in 0..=s.len() {
        for j in i..=s.len() {
            let sc = &s[i..j];
            let len = sc.len();
            let mid = (len / 2) as usize;
            let rev = sc[mid..len].chars().rev().collect::<String>();

            if len % 2 != 0 && sc[0..=mid] == rev {
                poly.insert(sc.to_string(), len);
            } else if sc[0..mid] == rev {
                poly.insert(sc.to_string(), len);
            }
        }
    }

    let mut max = ("".to_string(), 0);
    'sort: for (k, v) in poly {
        if max.1 < v {
            max = (k, v);
            continue 'sort;
        }
    }

    max.0
}

fn main() {
    assert_eq!(longest_palindrome("babad".to_string()), "aba".to_string());
    assert_eq!(longest_palindrome("cbbd".to_string()), "bb".to_string());
    assert_eq!(longest_palindrome("bc".to_string()), "b".to_string());
    assert_eq!(longest_palindrome("b".to_string()), "b".to_string());
    assert_eq!(longest_palindrome("mwwfjysbkebpdjyabcfkgprtxpwvhglddhmvaprcvrnuxifcrjpdgnktvmggmguiiquibmtviwjsqwtchkqgxqwljouunurcdtoeygdqmijdympcamawnlzsxucbpqtuwkjfqnzvvvigifyvymfhtppqamlgjozvebygkxawcbwtouaankxsjrteeijpuzbsfsjwxejtfrancoekxgfyangvzjkdskhssdjvkvdskjtiybqgsmpxmghvvicmjxqtxdowkjhmlnfcpbtwvtmjhnzntxyfxyinmqzivxkwigkondghzmbioelmepgfttczskvqfejfiibxjcuyevvpawybcvvxtxycrfbcnpvkzryrqujqaqhoagdmofgdcbhvlwgwmsmhomknbanvntspvvhvccedzzngdywuccxrnzbtchisdwsrfdqpcwknwqvalczznilujdrlevncdsyuhnpmheukottewtkuzhookcsvctsqwwdvfjxifpfsqxpmpwospndozcdbfhselfdltmpujlnhfzjcgnbgprvopxklmlgrlbldzpnkhvhkybpgtzipzotrgzkdrqntnuaqyaplcybqyvidwcfcuxinchretgvfaepmgilbrtxgqoddzyjmmupkjqcypdpfhpkhitfegickfszermqhkwmffdizeoprmnlzbjcwfnqyvmhtdekmfhqwaftlyydirjnojbrieutjhymfpflsfemkqsoewbojwluqdckmzixwxufrdpqnwvwpbavosnvjqxqbosctttxvsbmqpnolfmapywtpfaotzmyjwnd".to_string()), "khvhk".to_string());
    
}