Longest Palindromic Substring

public class Solution {
    public String longestPalindrome(String s) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        int n = s.length();
        if (n == 0) return "";
        String longest = String.valueOf(s.charAt(0));  // a single char itself is a palindrome
        for (int i = 0; i < n-1; i++) {
            String p1 = expandAroundCenter(s, i, i);
            if (p1.length() > longest.length())
                longest = p1;
         
            String p2 = expandAroundCenter(s, i, i+1);
            if (p2.length() > longest.length())
                longest = p2;
          }
          return longest;
    }
    
    private String expandAroundCenter(String s, int c1, int c2) {
      int l = c1, r = c2;
      int n = s.length();
      while (l >= 0 && r <= n-1 && s.charAt(l) == s.charAt(r)) {
        l--;
        r++;
      }
      return s.substring(l+1, r);
    }

}

 

O(n²) level 1

Manacher’s algorithm O(n) level 5

http://blog.csdn.net/insistgogo/article/details/12287805