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export default function longestPalindrome(s: string): string {    if (s.length < 2) return s;    const length = s.length;    let ans = "";    let i = 0;    while (i < length) {        const str1 = expand(s, i, i);        const str2 = expand(s, i, i + 1);        ans = [str1, str2].reduce((p, v) => (p.length > v.length ? p : v), ans);        if (ans === s) return s;        i = i + 1;    }    return ans;}
function expand(s: string, i: number, j: number): string {    while (i >= 0 && j < s.length && s[i] === s[j]) {        i--;        j++;    }
    const str = s.slice(i + 1, j);
    return str;}/* function longestPalindrome(s: string): string {    if (s.length < 2) return s;    const length = s.length;    let max_length = 1;    let start = 0;    const cache = new Array<boolean>(length * (length + 1) / 2);    function isPalindromic(i: number, j: number): boolean {        const key = i >= j ? (i * (i + 1) / 2) + j : (j * (j + 1) / 2) + i;        const cached = cache[key];        if (typeof cached !== "undefined") {            return cached;        }        const result = i === j            ? true            : i + 1 === j            ? s[i] === s[j]            : s[i] === s[j] && isPalindromic(i + 1, j - 1);        cache[key] = result;        return result;    }
    for (let i = 0; i < s.length; i++) {        for (let j = i; j < s.length; j++) {            // console.log(i, j)            if (i <= j && isPalindromic(i, j) && j - i + 1 > max_length) {                max_length = j - i + 1;                start = i;            }        }    }
    return s.slice(start, start + max_length);} */