KMP算法

public class KMP {
  public static int getIndexOf(String s, String m) {
    if (s == null || m == null || m.length() < 1 || s.length() < m.length())
      return -1;

    char[] str1 = s.toCharArray();
    char[] str2 = m.toCharArray();
    int i1 = 0, i2 = 0;
    int[] next = getNextArray(str2);
    while (i1 < str1.length && i2 < str2.length) {
      if (str1[i1] == str2[i2]) {
        i1++;
        i2++;

      } else if (next[i2] == -1) {
        i1++;
      } else {
        i2 = next[i2];
      }
    }

    return i2 == str2.length ? i1 - i2 : -1;
  }

  public static int[] getNextArray(char[] ms) {
    if (ms.length == 1)
      return new int[] {-1};

    int[] next = new int[ms.length];
    next[0] = -1;
    next[1] = 0;
    int i = 2;
    int cn = 0;
    while (i < next.length) {
      if (ms[i - 1] == ms[cn])
        next[i++] = ++cn;
      else if (cn > 0)
        cn = next[cn];
      else
        next[i++] = 0;
    }
    return next;
  }
}