原题:https://leetcode-cn.com/problems/longest-palindromic-substring/
给你一个字符串 s,找到 s 中最长的回文子串。
示例 1:
输入:s = "babad"
输出:"bab"
解释:"aba" 同样是符合题意的答案。
示例 2:输入:s = "cbbd"
输出:"bb"
示例 3:输入:s = "a"
输出:"a"
示例 4:输入:s = "ac"
输出:"a"
1.首先判断是否为空
2.考虑到存在多种情况(abba;abcba;abbba)
3.左右对比
public class Solution { public string LongestPalindrome(string s) { if (s == null || s.Length <= 1) //s的长度为空或1 { return s; } string result = s[0].ToString(); int max = 0; int maxLeft = 0; int maxRight = 0; for (int i = 1; i < s.Length; i++) { int left = i - 1; int right = i + 1; while (left >= 0) //执行0次abcba形回文判别;1次abba形回文判别;2次为abbba形判别。依次推 { if (s[left] == s[i]) { if (i - left > max) //判断是否为最长 { maxLeft = left; maxRight = i; max = i - left; } left--; continue; } else { break; } } while (left >= 0 && right < s.Length)//判断左右是否相等 { if (s[left] == s[right]) { if (right - left > max) { maxLeft = left; maxRight = right; max = right - left; } left--; right++; continue; } else { break; } } } if (max > 0) { result = ""; for (int i = maxLeft; i <= maxRight; i++) { result += s[i]; } } return result; } }