数据结构KMP实现
数据结构KMP实现
代码如下：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define N 100
void cal_next( char * str, int * next, int len )
//next数组作用返回失配位之前的最长公共前后缀！; len为返回当前的最长公共前后缀长度
{
int i, j;
next[0] = -1;
for( i = 1; i < len; i++ )
{
j = next[ i - 1 ];
while( str[ j + 1 ] != str[ i ] && ( j >= 0 ) )
{
j = next[ j ];
}
if( str[ i ] == str[ j + 1 ] )
{
next[ i ] = j + 1;
}
else
{
next[ i ] = -1;
}
}
}
int KMP( char * str, int slen, char * ptr, int plen, int * next )
{
int s_i = 0, p_i = 0;
while( s_i < slen && p_i < plen )
{
if( str[ s_i ] == ptr[ p_i ] )
{
s_i++;
p_i++;
}
else
{
if( p_i == 0 )
{
s_i++;
}
else
{
p_i = next[ p_i - 1 ] + 1;
}
}
}
return ( p_i == plen ) ? ( s_i - plen ) : -1;
}
int main()
{
char str[ N ] = {0};
char ptr[ N ] = {0};
int slen, plen;
int next[ N ];
while( scanf( "%s%s", str, ptr ) )
{
slen = strlen( str );
plen = strlen( ptr );
cal_next( ptr, next, plen );
printf( "%d\n", KMP( str, slen, ptr, plen, next ) );
}
return 0;
}