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Add Rabin-Karp search algorithm

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danghai 2019-05-10 17:39:48 -07:00
parent 495650023b
commit bb7199d706
1 changed files with 65 additions and 0 deletions
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searching/pattern_search/rabin_karp_search.c Normal file
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#include <stdio.h>
#include <string.h>
/* Kabin-Karp algorithm for pattern searching
d: radix-d notation. Ex. number from 0->9, d = 10
q: prime number for hashing */
void rabin_karp_search(char *str, char *pattern, int d, int q)
{
int len_str = strlen(str);
int len_pat = strlen(pattern);
int i, h = 1;
int hash_s = 0; /* hash value for string text */
int hash_p = 0; /* hash value for pattern */
/* h = pow(d, len_pat - 1) % q */
for(i = 0; i < len_pat - 1; i++)
h = d * h % q;
/* Calculating hashing of pattern and the 1st window of text */
for(i = 0; i < len_pat; i++)
{
hash_p = (d*hash_p + pattern[i]) % q;
hash_s = (d*hash_s + str[i]) % q;
}
for(i = 0; i <= len_str - len_pat; i++)
{
/* Check hash value of current window of text, and pattern
If it is match, check each character to make sure pattern
is match with current window of text */
if (hash_p == hash_s)
{
int j;
for(j = 0; j < len_pat; j++)
{
if(pattern[j] != str[i + j])
break;
}
if(len_pat == j)
printf("--Pattern is found at: %d\n", i);
}
/* Calculate hash value for next window by removing the leading
element of current window text, and adding its trailing */
hash_s = (d*(hash_s -str[i]*h) + str[i + len_pat]) % q;
/* Converting hash value to positive when it is negative */
if (hash_s < 0)
hash_s = hash_s + q;
}
}
int main()
{
char str[] = "AABCAB12AFAABCABFFEGABCAB";
char pat1[] = "ABCAB";
char pat2[] = "FFF"; /* not found */
char pat3[] = "CAB";
printf("String test: %s\n", str);
printf("Test1: search pattern %s\n", pat1);
rabin_karp_search(str, pat1, 256, 29);
printf("Test2: search pattern %s\n", pat2);
rabin_karp_search(str, pat2, 256, 29);
printf("Test3: search pattern %s\n", pat3);
rabin_karp_search(str, pat3, 256, 29);
return 0;
}