package com.xinyue.cross.server.server;

public class MessageHandler {

public static void main(String[] args) {

String s = "bb";

MessageHandler m = new MessageHandler();

String longest = m.getLongest(s);

System.out.println(longest);

}

private String getLongest(String s) {

char[] helpChar = getHelpChar(s);

return getLongest(helpChar);

}

private char[] getHelpChar(String s) {

char[] c = s.toCharArray();

int l = c.length;

int helpLength = 2 * l + 1;

char[] helpChar = new char[helpLength];

for (int i = 0; i < helpLength; i++) {

if (i % 2 == 0) {

helpChar[i] = '#';

} else {

helpChar[i] = c[i / 2];

}

}

return helpChar;

}

private String getLongest(char[] helpChar) {

int maxRadius = 0;

int index = 0;

for (int i = 0; i < helpChar.length; i++) {

int radius = 0;

while (i - radius >= 0 && i + radius <= helpChar.length - 1) {

if (helpChar[i - radius] == helpChar[i + radius]) {

if (radius > maxRadius) {

maxRadius = radius;

index = i;

}

radius++;

} else {

break;

}

}

}

int upper = index + maxRadius;

int lower = index - maxRadius;

char[] subArray = getSubArray(helpChar, lower, upper);

char[] chars = filterHelpChar(subArray);

return new String(chars);

}

private char[] getSubArray(char[] c, int lower, int upper) {

int length = upper - lower + 1;

char[] chars = new char[length];

for (int i = 0; i < length; i++) {

chars[i] = c[lower + i];

}

return chars;

}

private char[] filterHelpChar(char[] c) {

int length = c.length / 2;

char[] chars = new char[length];

for (int i = 0; i < length; i++) {

chars[i] = c[2 * i + 1];

}

return chars;

}

}