KMP模式匹配算法

<pre name="code" class="cpp">#include<iostream>
#include<vector>
#include<string.h>

using namespace std;

void get_next(vector<int>& next,const char* subStr)
{
	int length=next.size();
	next[0]=-1;                    //next[0] = -1
	int i=0,j=-1;
	while(i<length-1)                     //i<length-1,为循环限制条件
	{
		if(j==-1 || subStr[i]==subStr[j])
		{
			next[++i] = ++j;           
		} 
		else
			j = next[j];                 //数组适当进行回退
	}
}

int kmpMatch(const char* str,const char* substr)
{
	int lengthS=strlen(str);
	int length=strlen(substr);
	
	vector<int> next(length,0);
	get_next(next,substr);
	
	int i=0;
	int j=0;
	while(i<lengthS && j<length)
	{
		if(j==-1 || str[i]==substr[j])//j==-1也是就回退到了子串的开头位置，则i,j都向前一步
		{                              //假设主串和子串匹配，也须要向前一步
			i++;
			j++;
		}
		else
		{
			j=next[j];//假设未能匹配则回退到下一位置
		}
	}
	if(j==length)//已经查找到子串的末尾
		return i-length;
	else
		return 0;
}

int main()
{
	const char* str="abcababcabcabx";
	const char* subStr="abcabx";
	cout<<kmpMatch(str,subStr)<<endl;
	return 0;
}