Oct 20, 2011

C Program to search the perticulur pattern in the string using Horspool method.

C Program to find the substring in a String using the Horspool method. This algorithm uses the Brute-Forse method which searches the text between 0 and n-m, and after each cycle it shifts the pattern by one position to the right. Read more about C Programming Language .

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#include<stdio.h>
#include<string.h>
#include<conio.h>
#define MAX 500
int t[MAX];
void shifttable(char p[])
{
 int i,j,m;
 m=strlen(p);
 for(i=0;i<MAX;i++)
  t[i]=m;
 for(j=0;j<m-1;j++)
  t[p[j]]=m-1-j;
}
int horspool(char src[],char p[])
{
 int i,j,k,m,n;
 n=strlen(src);
 m=strlen(p);
 printf("\nLength of text=%d",n);
 printf("\n Length of pattern=%d",m);
 i=m-1;
 while(i<n)
 {
  k=0;
  while((k<m)&&(p[m-1-k]==src[i-k]))
   k++;
  if(k==m)
   return(i-m+1);
  else
   i+=t[src[i]];
 }
 return -1;
}
void main()
{
 char src[100],p[100];
 int pos;
 clrscr();
 printf("Enter the text in which pattern is to be searched:\n");
 gets(src);
 printf("Enter the pattern to be searched:\n");
 gets(p);
 shifttable(p);
 pos=horspool(src,p);
 if(pos>=0)
  printf("\n The desired pattern was found starting from position %d",pos+1);
 else
  printf("\n The pattern was not found in the given text\n");
 getch();
}
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