package string; import java.util.Random; import java.util.UUID; //最长回文字符串，中心阔山算法 public class CenterExpansionAlgorithm { private static final String ALPHABET = "abcdefghijklmnopqrstuvwxyz"; public static String generateRandomString(int length) { Random random = new Random(); StringBuilder sb = new StringBuilder(length); for (int i = 0; i < length; i++) { int index = random.nextInt(ALPHABET.length()); char randomChar = ALPHABET.charAt(index); sb.append(randomChar); } return sb.toString(); } public static void main(String[] args) { for (int i = 0; i < 20 ; i++) { String s = generateRandomString(20); System.out.println(s); String s1 = new CenterExpansionAlgorithm().longestPalindrome(s); System.out.println(s1); } } //获取字符串最长回文 public String longestPalindrome(String s){ if(s == null || s.length() < 1){ return null; } int start = 0,end = 0,length = 0; for (int i = 0; i < s.length(); i++) { int i1 = expandAroundCenter(s, i, i); int i2 = expandAroundCenter(s, i, i + 1); //获取最大长度 length = Math.max(i1, i2); if (length > end - start + 1){ start = i - (length - 1)/2; end = i + length/2; } // if(end - start < length){ // start = i-(length/2); // if(length % 2 == 0){ // start++; // } // end = start + length; // } } return s.substring(start,end+1); } /** * 环绕中心扩展 */ public int expandAroundCenter(String s,int left,int right){ while (left >= 0 && right< s.length() && s.charAt(left) == s.charAt(right)){ left--; right++; } return right - left -1; } }