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));
}
}