題目
Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.
Example 1:
Input: "babad"
Output: "bab"
Note: "aba" is also a valid answer.
Example 2:
Input: "cbbd"
Output: "bb"
O(n^2)級(jí)別的解法
使用遍歷的方法格嗅，從左往右依次尋找躲株，尋找的基本思想是先從一個(gè)字母開始，如果左邊索引對(duì)應(yīng)的數(shù)等于右邊索引對(duì)應(yīng)的數(shù)籽懦，則擴(kuò)展左邊索引和右邊索引暴拄，左減1漓滔，右加1，直到左邊或右邊達(dá)到邊界乖篷。并且記錄相應(yīng)的左邊索引和子串的長(zhǎng)度响驴。
代碼示例
public class Solution {
private int lo, maxLen;
public String longestPalindrome(String s) {
int len = s.length();
if (len < 2)
return s;
for (int i = 0; i < len-1; i++) {
extendPalindrome(s, i, i); //assume odd length, try to extend Palindrome as possible
extendPalindrome(s, i, i+1); //assume even length.
}
return s.substring(lo, lo + maxLen);
}
private void extendPalindrome(String s, int j, int k) {
while (j >= 0 && k < s.length() && s.charAt(j) == s.charAt(k)) {
j--;
k++;
}
if (maxLen < k - j - 1) {
lo = j + 1;
maxLen = k - j - 1;
}
}}
