kmp算法,求重复字符串

public class Demo {
    public static void main(String[] args) {
        String s1 = "ADBCFHABESCACDABCDABCE";
        String s2 = "ABCDABCE";
        int i = kmp(s1, s2);
        System.out.println("下标 i="+i+"  对应字符串："+s1.substring(14));
    }

    public static int kmp(String s1, String s2) {
        char[] c1 = s1.toCharArray();
        char[] c2 = s2.toCharArray();
        int[] next=getNext(s2);
        int i=0,j=0;
        while (i < c1.length && j <c2.length)
        {
            if (j == -1 || c1[i] == c2[j]) {
                i++;
                j++;
            } else {
                j = next[j];
            }
        }
        if (j == c2.length)
            return i - j;
        else
            return -1;
    }

    public static int[] getNext(String s) {
        char[] chars = s.toCharArray();
        int[] arr = new int[chars.length];
        arr[0] = -1;
        int k = -1;
        int j = 0;
        while (j < chars.length - 1) {
            //chars[k]表示前缀，chars[j]表示后缀
            if (k == -1 || chars[j] == chars[k]) {
                ++k;
                ++j;
                arr[j] = k;
            } else {
                k = arr[k];
            }
            System.out.println(Arrays.toString(arr));
        }
        return arr;
    }
}