KMP算法（模式匹配算法）

KMP算法利用部分匹配结果避免指针回溯，具体是next数组或者改良后的nextval数组实现；
next的实现利用递推的思想，比较抽象，不容易理解。

include <stdio.h>

#include <string>
void Get_Next(char* str, int* next)
{
	int len = strlen(str);

	int i = 0, j = -1; next[0] = -1;
	while (i < len)
	{
		if (j == -1 || str[i] == str[j]) {
			j++; i++; next[i] = j;
		}
		else j = next[j];
	}
}

void Get_NextVal(char* str, int* nextval)
{
	int len = strlen(str);
	int i = 0, j = -1;
	nextval[0] = -1;
	while (i < len)
	{
		if (j == -1 || str[i] == str[j])
		{
			i++; j++;
			if (str[i] == str[j]) nextval[i] = nextval[j];
			else nextval[i] = j;
		}
		else j = nextval[j];
	}
}

int Index_KMP(char* Str1, char* Str2,int* next)
{
	int i = 0, j = 0;
	int len1 = strlen(Str1), len2 = strlen(Str2);
	while (i < len1 && j < len2)
	{
		if (j == -1 || Str1[i] == Str2[j])
		{
			i++; j++;
		}
		else j = next[j];
	}
	if (j >= len2) return i - len2;
	else return 0;
}



int main()
{
	char str[] = "ababcabcacbab";
	char Str[] = "abcac";
	int len = strlen(Str);
	int* next = (int*)malloc(sizeof(int) * len);
	Get_Next(Str, next);
	int* nextval = (int*)malloc(sizeof(int) * len);
	Get_NextVal(Str, nextval);
	printf("%d\n", Index_KMP(str,Str,nextval));
}