#include < stdio.h >
#include < string.h >
#include < stdlib.h >
void computeLPSArray(char *pat, int M, int *lps);
void KMPSearch(char *pat, char *txt)
{
int M =
strlen(pat);
int N =
strlen(txt);
// create lps[] that
will hold the longest prefix suffix values for pattern
int *lps = (int
*)malloc(sizeof(int)*M);
int j
= 0; // index for pat[]
// Preprocess the
pattern (calculate lps[] array)
computeLPSArray(pat, M,
lps);
int i = 0;
// index for txt[]
while(i < N)
{
if(pat[j] == txt[i])
{
j++;
i++;
}
if (j
== M)
{
printf("Found pattern at index %d \n",
i-j);
j = lps[j-1];
}
//
mismatch after j matches
else
if(pat[j] != txt[i])
{
// Do not match lps[0..lps[j-1]]
characters,
// they will match anyway
if(j != 0)
j = lps[j-1];
else
i = i+1;
}
}
free(lps); // to avoid
memory leak
}
void computeLPSArray(char *pat, int M, int *lps)
{
int len = 0;
// lenght of the previous longest prefix
suffix
int i;
lps[0] = 0; // lps[0] is
always 0
i = 1;
// the loop calculates
lps[i] for i = 1 to M-1
while(i < M)
{
if(pat[i] == pat[len])
{
len++;
lps[i] = len;
i++;
}
else // (pat[i] != pat[len])
{
if( len != 0 )
{
// This is
tricky. Consider the example AAACAAAA and i = 7.
len =
lps[len-1];
// Also,
note that we do not increment i here
}
else // if (len == 0)
{
lps[i] =
0;
i++;
}
}
}
}
// Driver program to test above function
int main()
{
char *txt =
"ABABDABACDABABCABAB";
char *pat =
"ABABCABAB";
KMPSearch(pat,
txt);
return 0;
}