问最长平方子串的算法

EN

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;

public class LongestPalindrome 
{
	// function to pre-process string 
	public String preProcess(String str) 
	{
		int len = str.length();
		if (len == 0)
		{
			return "^$";
		}
		String s = "^";
		for (int i = 0; i < len; i++)
		{
			s += "#" + str.charAt(i);    
		}
		s += "#$";
		return s;
	}
	
	// function to get largest palindrome sub-string 
	public String getLongestPalindrome(String str)
	{
		// pre-process string 
		char[] s = preProcess(str).toCharArray();
		int N = s.length;
		int[] p = new int[N + 1];
		int id = 0; 
		int mx = 0;
		for (int i = 1; i < N - 1; i++) 
		{
			p[i] = 0;
			while (s[i + 1 + p[i]] == s[i - 1 - p[i]])
			{
				p[i]++;
			}
			if (i + p[i] > mx) 
			{
				mx = i + p[i];
				id = i;
			}
		}
		// length of largest palindrome 
		int maxLen = 0;
		// position of center of largest palindrome 
		int centerIndex = 0;
		for (int i = 1; i < N - 1; i++) 
		{
			if (p[i] > maxLen) 
			{
				maxLen = p[i];
				centerIndex = i;
			}
		}
		// starting index of palindrome 
		int pos = (centerIndex - 1 - maxLen)/2;
		return str.substring(pos , pos + maxLen);        
	}
	
	// Main Function
	public static void main(String[] args) throws IOException
	{    
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		System.out.println("LongestPalindrome Algorithm Test\n");
		System.out.println("\nEnter String");
		String text = br.readLine();
		
		LongestPalindrome m = new LongestPalindrome(); 
		String LongestPalindrome = m.getLongestPalindrome(text); 
		System.out.println("\nLongest Palindrome: "+ LongestPalindrome);    
	}    
}