我编写了以下函数来查找字符串中最长的回文。它工作正常，但它不会像＃34;中午＆＃34;或者＆＃34; redder＆＃34;。我摆弄并改变了for循环中的第一行：
var oddPal = centeredPalindrome(i, i);
到
var oddPal = centeredPalindrome(i-1, i);
现在它有效，但我不清楚为什么。我的直觉是，如果你正在检查一个奇怪的回文，它将在开始时有一个额外的字符（我把它白板化了，这就是我得出的结论）。我的理由是否在正确的轨道上？
var longestPalindrome = function(string) {
var length = string.length;
var result = "";
var centeredPalindrome = function(left, right) {
while (left >= 0 && right < length && string[left] === string[right]) {
//expand in each direction.
left--;
right++;
}
return string.slice(left + 1, right);
};
for (var i = 0; i < length - 1; i++) {
var oddPal = centeredPalindrome(i, i);
var evenPal = centeredPalindrome(i, i);
if (oddPal.length > result.length)
result = oddPal;
if (evenPal.length > result.length)
result = evenPal;
}
return "the palindrome is: " + result + " and its length is: " + result.length;
};
更新： 在保罗真棒answer之后，我认为为了清晰起见改变这两个变量是有意义的：
var oddPal = centeredPalindrome(i-1, i + 1);
var evenPal = centeredPalindrome(i, i+1);
答案 0 :(得分：7)
你有倒退 - 如果你输出＆＃34;奇数＆＃34;回文（你的修复）你会发现他们实际上是偶数。
想象一下＆＃34;中午＆＃34;，从第一个＆＃34; o＆＃34;开始（左和右）。匹配，然后你移动它们 - 现在你正在比较第一个＆＃34; n＆＃34;到第二个＆＃34; o＆＃34;。不好。但是通过修复，你开始比较两个＆＃34; o＆＃34; s，然后转移到＆＃34; n＆＃34; s。
示例（使用var oddPal = centeredPalindrome(i-1, i);修正）：
var longestPalindrome = function(string) {
var length = string.length;
var result = "";
var centeredPalindrome = function(left, right) {
while (left >= 0 && right < length && string[left] === string[right]) {
//expand in each direction.
left--;
right++;
}
return string.slice(left + 1, right);
};
for (var i = 0; i < length - 1; i++) {
var oddPal = centeredPalindrome(i, i + 1);
var evenPal = centeredPalindrome(i, i);
if (oddPal.length > 1)
console.log("oddPal: " + oddPal);
if (evenPal.length > 1)
console.log("evenPal: " + evenPal);
if (oddPal.length > result.length)
result = oddPal;
if (evenPal.length > result.length)
result = evenPal;
}
return "the palindrome is: " + result + " and its length is: " + result.length;
};
console.log(
longestPalindrome("nan noon is redder")
);
答案 1 :(得分：0)
如果早期发现最大的回文，这将是最佳的。 一旦发现它将退出两个循环。
function isPalindrome(s) {
//var rev = s.replace(/\s/g,"").split('').reverse().join(''); //to remove space
var rev = s.split('').reverse().join('');
return s == rev;
}
function longestPalind(s) {
var maxp_length = 0,
maxp = '';
for (var i = 0; i < s.length; i++) {
var subs = s.substr(i, s.length);
if (subs.length <= maxp_length) break; //Stop Loop for smaller strings
for (var j = subs.length; j >= 0; j--) {
var sub_subs = subs.substr(0, j);
if (sub_subs.length <= maxp_length) break; // Stop loop for smaller strings
if (isPalindrome(sub_subs)) {
maxp_length = sub_subs.length;
maxp = sub_subs;
}
}
}
return maxp;
}
答案 2 :(得分：0)
链接到 gist
使用动态编程。将每个问题分解为自己的方法，然后采用每个问题的解决方案并将它们加在一起得到答案。
class Palindrome {
constructor(chars){
this.palindrome = chars;
this.table = new Object();
this.longestPalindrome = null;
this.longestPalindromeLength = 0;
if(!this.isTheStringAPalindrome()){
this.initialSetupOfTableStructure();
}
}
isTheStringAPalindrome(){
const reverse = [...this.palindrome].reverse().join('');
if(this.palindrome === reverse){
this.longestPalindrome = this.palindrome;
this.longestPalindromeLength = this.palindrome.length;
console.log('pal is longest', );
return true;
}
}
initialSetupOfTableStructure(){
for(let i = 0; i < this.palindrome.length; i++){
for(let k = 0; k < this.palindrome.length; k++){
this.table[`${i},${k}`] = false;
}
}
this.setIndividualsAsPalindromes();
}
setIndividualsAsPalindromes(){
for(let i = 0; i < this.palindrome.length; i++){
this.table[`${i},${i}`] = true;
}
this.setDoubleLettersPlaindrome();
}
setDoubleLettersPlaindrome(){
for(let i = 0; i < this.palindrome.length; i++){
const firstSubstring = this.palindrome.substring(i, i + 1);
const secondSubstring = this.palindrome.substring(i+1, i + 2);
if(firstSubstring === secondSubstring){
this.table[`${i},${i + 1}`] = true;
if(this.longestPalindromeLength < 2){
this.longestPalindrome = firstSubstring + secondSubstring;
this.longestPalindromeLength = 2;
}
}
}
this.setAnyPalindromLengthGreaterThan2();
}
setAnyPalindromLengthGreaterThan2(){
for(let k = 3; k <= this.palindrome.length; k++){
for(let i = 0; i <= this.palindrome.length - k; i++){
const j = i + k - 1;
const tableAtIJ = this.table[`${i+1},${j-1}`];
const stringToCompare = this.palindrome.substring(i, j +1);
const firstLetterInstringToCompare = stringToCompare[0];
const lastLetterInstringToCompare = [...stringToCompare].reverse()[0];
if(tableAtIJ && firstLetterInstringToCompare === lastLetterInstringToCompare){
this.table[`${i},${j}`] = true;
if(this.longestPalindromeLength < stringToCompare.length){
this.longestPalindrome = stringToCompare;
this.longestPalindromeLength = stringToCompare.length;
}
}
}
}
}
printLongestPalindrome(){
console.log('Logest Palindrome', this.longestPalindrome);
console.log('from /n', this.palindrome );
}
toString(){
console.log('palindrome', this.palindrome);
console.log(this.table)
}
}
// const palindrome = new Palindrome('lollolkidding');
// const palindrome = new Palindrome('acbaabca');
const palindrome = new Palindrome('acbaabad');
palindrome.printLongestPalindrome();
//palindrome.toString();
答案 3 :(得分：0)
public static String getDomainNameWithGuava(String url) throws MalformedURLException,
URISyntaxException {
String host =new URL(url).getHost();
String domainName="";
try{
domainName = InternetDomainName.from(host).topPrivateDomain().toString();
}catch (IllegalStateException | IllegalArgumentException e){
domainName= getDomain(url,true);
}
return domainName;
}
答案 4 :(得分：0)
function longest_palindrome(s) {
if (s === '') {
return ''
}
let arr = [];
let _s = s.split('');
for (let i = 0; i < _s.length; i++) {
for (let j = 0; j < _s.length; j++) {
let word = _s.slice(0, j + 1).join('');
let rev_word = _s.slice(0, j + 1).reverse().join('');
if (word === rev_word) {
arr.push(word)
}
}
_s.splice(0, 1)
}
let _arr = arr.sort((a, b) => a.length - b.length);
for (let i = 0; i < _arr.length; i++) {
if (_arr[arr.length - 1].length === _arr[i].length) {
return _arr[i]
}
}
}
longest_palindrome（'bbaaacc'） //此代码将为您提供字符串中第一个最长的回文子字符串
答案 5 :(得分：0)
public string LongestPalindrome(string s) {
return LongestPalindromeSol(s, 0, s.Length-1);
}
public static string LongestPalindromeSol(string s1, int start, int end)
{
if (start > end)
{
return string.Empty;
}
if (start == end)
{
char ch = s1[start];
string s = string.Empty;
var res = s.Insert(0, ch.ToString());
return res;
}
if (s1[start] == s1[end])
{
char ch = s1[start];
var res = LongestPalindromeSol(s1, start + 1, end - 1);
res = res.Insert(0, ch.ToString());
res = res.Insert(res.Length, ch.ToString());
return res;
}
else
{
var str1 = LongestPalindromeSol(s1, start, end - 1);
var str2 = LongestPalindromeSol(s1, start, end - 1);
if (str1.Length > str2.Length)
{
return str1;
}
else
{
return str2;
}
}
}
答案 6 :(得分：0)
let str = "HYTBCABADEFGHABCDEDCBAGHTFYW12345678987654321ZWETYGDE";
let rev = str.split("").reverse().join("").trim();
let len = str.length;
let a="";
let result = [];
for(let i = 0 ; i < len ; i++){
for(let j = len ; j > i ; j--){
a = rev.slice(i,j);
if(str.includes(a)){
result.push(a);
break;
}
}
}
result.sort((a,b) => { return b.length - a.length})
let logPol = result.find((value)=>{
return value === value.split('').reverse().join('') && value.length > 1
})
console.log(logPol);答案 7 :(得分：-3)
This is in JS ES6. much simpler and works for almost all words .. Ive tried radar, redder, noon etc.
const findPalindrome = (input) => {
let temp = input.split('')
let rev = temp.reverse().join('')
if(input == rev){
console.log('Palindrome', input.length)
}
}
//i/p : redder
// "Palindrome" 6