kmp算法

public class KMP2 {
    static int[] getNext(String str) {
        char[] charArray = str.toCharArray();
        int len = charArray.length;
        if (len == 1) return new int[]{-1};
        int[] next = new int[len];
        next[0] = -1;
        next[1] = 0;
        int i = 2, cn = 0;
        while (i < len) {
            if (charArray[cn] == charArray[i - 1]) {
                next[i++] = ++cn;
            } else if (cn > 0) {
                cn = next[cn];
            } else {
                next[i++] = 0;
            }
        }
        return next;
    }

    static int indexOf(String str1, String str2) {
        char[] char1 = str1.toCharArray();
        char[] char2 = str2.toCharArray();
        int len1 = char1.length, len2 = char2.length;
        int[] next = getNext(str2);
        int i = 0, j = 0;
        while (i < len1 && j < len2) {
            if (char1[i] == char2[j]) {
                i++;
                j++;
            } else if (j > 0) {
                j = next[j];
            } else {
                i++;
            }
        }
        return j < len2 ? -1 : i - j;
    }

    public static void main(String[] args) {
        System.out.println(indexOf("123", "23"));
        System.out.println(indexOf("123", "3"));
        System.out.println(indexOf("123", "5"));
        System.out.println(indexOf("aabaaabaaac", "aabaaac"));
    }
}