【LeetCode】#5最長迴文子串(Longest Palindromic Substring)
阿新 • • 發佈:2018-12-03
【LeetCode】#5最長迴文子串(Longest Palindromic Substring)
題目描述
給定一個字串 s,找到 s 中最長的迴文子串。你可以假設 s 的最大長度為 1000。
示例
示例 1:
輸入: “babad”
輸出: “bab”
注意: “aba” 也是一個有效答案。
示例 2:
輸入: “cbbd”
輸出: “bb”
Description
Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.
Example
Example 1:
Input: “babad”
Output: “bab”
Note: “aba” is also a valid answer.
Example 2:
Input: “cbbd”
Output: “bb”
解法
class Solution{ public String longestPalindrome(String s){ if(s==null || s.length()<1) return ""; int start = 0, end = 0; for(int i=0; i<s.length(); i++){ int len1 = expandAroundCenter(s, i, i); int len2 = expandAroundCenter(s, i, i+1); int len = Math.max(len1, len2); if(len>end-start){ start = i - (len-1)/2; end = i + len/2; } } return s.substring(start, end+1); } private int expandAroundCenter(String s, int left, int right){ int L = left, R = right; while(L>=0 && R<s.length() && s.charAt(L)==s.charAt(R)){ L--; R++; } return R-L-1; } }