马拉车算法-求解最长回文字符串

import java.util.*;

public class Main{
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        String s = sc.nextLine();
        System.out.println(fun(s));
    }
    private static String fun(String s){
        int len = s.length();
        char[] c = new char[2*len+2];
        c[0]='$';
        c[1]='#';
        int index = 2;
        for(int i=0;i<len;i++){
            c[index++]=s.charAt(i);
            c[index++]='#';
        }
        len = 2*len+2;
        int maxmid = 0;
        int maxright = 0;
        int curmid = 0;
        int curlength = 0;
        int[] dp = new int[len];
        for(int i=1;i<len;i++){
            dp[i]=i<maxright?Math.min(maxright-i,dp[2*maxmid-i]):1;
            while(i+dp[i]<len && i-dp[i]>=0 && c[i+dp[i]]==c[i-dp[i]]){
                dp[i]++;
            }
            if(maxright<i+dp[i]){
                maxright=i+dp[i];
                maxmid=i;
            }
            if(curlength<dp[i]){
                curlength=dp[i];
                curmid=i;
            }
        }
        return s.substring((curmid-curlength)/2,(curmid-curlength)/2+curlength-1);
    }
}