给定一个字符串str，只能在str的后面添加字符，生成一个更长的字符串，更长的字符串需要
包含两个str，且两个str开始的位置不能一样。求最少添加多少个字符。

 

 

 

其实就是求终止字符的next数组 

kmp

 

知道了最大共用-》最少添加

public class Main{
 
    public static String answer(String str) {
        if (str == null || str.length() == 0) {
            return "";
        }
        char[] chas = str.toCharArray();
        if (chas.length == 1) {
            return str + str;
        }
        if (chas.length == 2) {
            return chas[0] == chas[1] ? (str + String.valueOf(chas[0])) : (str + str);
        }
        int endNext = endNextLength(chas);
        return str + str.substring(endNext);
    }
 
    public static int endNextLength(char[] chas) {
        int[] next = new int[chas.length + 1];
        next[0] = -1;
        next[1] = 0;
        int pos = 2;
        int cn = 0;
        while (pos < next.length) {
            if (chas[pos - 1] == chas[cn]) {
                next[pos++] = ++cn;
            } else if (cn > 0) {
                cn = next[cn];
            } else {
                next[pos++] = 0;
            }
        }
        return next[next.length - 1];
    }
 
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String test1 = sc.nextLine();
        System.out.println(answer(test1).length()-test1.length());
    }
 
}