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;
	}
}