LeetCode-5 Longest Palindromic Substring(求最长回文子串)

Given a string S, find the longest palindromic substring in S. You may assume that the maximum length of S is 1000, and there exists one unique longest palindromic substring.

JAVA:

public class Solution {public static String longestPalindrome(String s) {String s1 = "";String s2 = "";int max = 0;int temp = 0;int iflag = 0;for (int i = 0; i < s.length(); i++) {//回文数为奇数个的情况。for (int j = 1; i - j >= 0 && i + j <= s.length() - 1; j++) {if (s.charAt(i + j) == s.charAt(i - j))temp++;else {break;}}if (temp > max) {max = temp;iflag = i;}temp = 0;}s1 = s.substring(iflag - max, iflag + max +1);max = 0;temp = 0;iflag = 0;for (int i = 0; i < s.length(); i++) {// 回文数为偶数个的情况。for (int j = 0; i - j >= 0 && i + j + 1 <= s.length() - 1; j++) {if (s.charAt(i - j) == s.charAt(i + j + 1))temp++;else {break;}}if (temp > max) {max = temp;iflag = i;}temp = 0;}s2 = s.substring(iflag - max +1, iflag + max +1);return s1.length()>s2.length()?s1:s2;//返回二者中更长的一个。}}

Runtime:245 ms

分析：

两种情况分开处理，分别是回文数为奇数个、回文数为偶数个的情况（因为二者判定条件不同，具体参考我上面的代码）。

比较要留意的是两种情况的substring位置的考虑。