KMP算法实现

核心是模式串next数组的生成

#include <stdio.h>
#include <string.h>
#define NS 100
int strpos( char s1[] , char s2[] ,int N[]);
void next( char s2[],int N[]);
int main(int argc, char *args[] )
{
    int i = 0,k = 0;
    int N[NS] = {0};
    next( args[2],N );
    printf("%d\n",strpos(args[1],args[2],N));
    return 0;
}

int strpos( char s1[],char s2[],int N[])
{
    int i = 0,j = 0,l=strlen(s1),l2=strlen(s2);
    if(l2 > l) 
    {
        printf("Error,pattern string is longer than source string.\n");
        return -2;
    }
    while( i < l )
    {
        if(s2[j] == '\0')
        {
            break;
        }
        if(s2[j] == s1[i])
        {
            j++;
            i++;
        }
        else
        {
            i -= N[j];
            j = 0;
        }
    }
    return (j > 0 && s2[j] =='\0') ? i-j : -1;
}
//模式串对应的回退数组，标记着主串在和模式串每个位置匹配失败后，主串应该回退多少位再和模式串逐一匹配
void next(char s2[],int N[])
{
    N[0] =  -1;
    N[1] =  0;
    int i = 1,j = -1,l=strlen(s2);
    while( i < l )
    {
        if(j== -1 || s2[i] == s2[j])
        {
            j++;
            i++;
            N[i] = j;
        }
        else
        {
            j = N[j];
        }
    }
}

#kmp abababacb ababacb
2

编译执行 kmp abababacb ababacb

结果为2