KMP算法

public int indexOf(String s, String m) {
        if (s == null || m == null || m.length() < 1 || s.length() < 1 || s.length() < m.length())
            return -1;
        char[] ss = s.toCharArray();
        char[] ms = m.toCharArray();
        int si = 0, mi = 0;
        int[] next = nextIndex(ms);
        while (si < ss.length && mi < ms.length) {
            if (mi == -1 || ss[si] == ms[mi]) {
                si++;
                mi++;
            } else {
                mi = next[mi];
            }
        }
        return mi == ms.length ? si - mi : -1;
    }

    public int[] nextIndex(char[] str) {
        if (str.length == 1)
            return new int[]{-1};
        int[] next = new int[str.length];
        next[0] = -1;
        next[1] = 0;
        int pos = 2;
        int cn = 0;
        while (pos < next.length) {
            if (str[pos - 1] == str[cn]) {
                next[pos++] = ++cn;
            } else if (cn > 0) {
                cn = next[cn];
            } else {
                next[pos++] = 0;
            }
        }
        return next;
    }