KMP算法Java实现

源代码如下所示：

package com.zuoshen;

public class Problem_02_KMPAlgorithm {

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

	public static int[] getNextArray(char[] ms) {
		if (ms.length == 1) {
			return new int[] { -1 };
		}
		int[] next = new int[ms.length];
		next[0] = -1;//规定0位置为-1
		next[1] = 0;//规定1位置为0
		int pos = 2;//标记从2开始的位置
		int cn = 0;//cn为跳的位置与(i+1)比较
		while (pos < next.length) {
			if (ms[pos - 1] == ms[cn]) {
				next[pos++] = ++cn;
			} else if (cn > 0) {
				cn = next[cn];//cn往前跳，继续找自己前面的前半段
			} else {
				next[pos++] = 0;//不存在前缀与后缀相等
			}
		}
		return next;
	}

	public static void main(String[] args) {
		String str = "abcabcababaccc";
		String match = "ababa";
		System.out.println(getIndexOf(str, match));

	}

}