KMP算法

KMP算法实现

#include <stdio.h>
#include <stdlib.h>

void buildNext(int* next, char* s2, int len2)
{
	int i=0;
	int j=-1;
	next[0] = -1;

	while(i<len2-1)
	{
		if(j==-1 || s2[i] == s2[j])
		{
			i++;
			j++;
			if(s2[i] != s2[j]) next[i] = j;
			else next[i]=next[j];
		}
		else
		{		
			j = next[j];
		}
	}
}

int KMP(char* s1, int len1, char* s2, int len2)
{
	int i=0;
	int j=0;
	int* next = (int*)malloc(len2*sizeof(int));

	buildNext(next,s2,len2);

	while(i<len1 && j<len2)
	{
		if(j==-1 || s1[i] == s2[j])
		{
			i++;
			j++;
		}
		else
		{
			j = next[j];
		}
	}

	free(next);
	if(j>=len2) return i-len2;
	else return -1;
}

int main()
{
	char s1[7] = {"aabaaab"};
	char s2[4] = {"ab"};
	int len1 = 7;
	int len2 = 2;
	int rtn;
	
	rtn = KMP(s1, len1, s2, len2);
	printf("%d", rtn);

	return 0;
}