KMP算法----java实现

字符串的模式匹配本文先实现最基本的回溯实现的已经KMP算法，BM算法后面博文继续实现。ps:本篇博文强烈参考了July大神的作品，地址http://blog.csdn.net/v_july_v/article/details/6545192.再次感激大神~~

1.最基本的回溯实现字符串模式匹配

package com.sheepmu;

public class KMPText
{
public static void main(String[] args)
{
String s0="abcdeabckkfgh";
String s1="abck";
char[] as0=s0.toCharArray();
char[] as1=s1.toCharArray();
System.out.println(getIndex(as0,as1));
}

public static int getIndex(char[] as0,char[] as1)
{
int len0=as0.length;
int len1=as1.length;
int i=0,j=0;
while(i<len0&&j<len1)
{
if(as0[i]==as1[j])
{
i++;
j++;
}
else
{
i=i-j+1;
j=0;
}
}
if(j>=len1)
{
return i-j;
}
return -1;
}
}

2.KMP算法实现字符串模式匹配

package com.sheepmu;

public class KMPText
{
public static void main(String[] args)
{
String s0="abcdeabckkfgh";
String s1="abcke";
char[] as0=s0.toCharArray();
char[] as1=s1.toCharArray();
System.out.println(getKMP(as0,as1));
}

public static int[] next(char[] as1)
{
int[] next=new int[as1.length];
next[0]=-1;
int len1=as1.length;
int i=0,j=-1;
while(i<len1-1)//!!!!!!!!!!!!!记得-1
{
if(j==-1||as1[i]==as1[j])
{
i++;
j++;
if(as1[i]!=as1[j])
{
next[i]=j;
}
else
{
next[i]=next[j];
}
}
else
{
j=next[j];
}
}
return next;
}

public static int getKMP(char[] as0,char[] as1)
{
int len0=as0.length;
int len1=as1.length;
int i=0,j=0;
int[] next=next(as1);
while(i<len0&&j<len1)
{
if(j==-1||as0[i]==as1[j])
{
i++;
j++;
}
else
{
j=next[j];
}
}
if(j>=len1)
{
return i-j;
}
return -1;
}
}