KMPAlgorithm.cpp

#include <bits/stdc++.h> 

void computeLPSArray(char* pat, int M, int* lps); 
void KMPSearch(char* pat, char* txt) 
{ 
	int M = strlen(pat); 
	int N = strlen(txt); 

	int lps[M];  
	computeLPSArray(pat, M, lps); 

	int i = 0; 
	int j = 0;  
	while (i < N) { 
		if (pat[j] == txt[i]) { 
			j++; 
			i++; 
		} 

		if (j == M) { 
			printf("Found pattern at index %d ", i - j); 
			j = lps[j - 1]; 
		} 

		 
		else if (i < N && pat[j] != txt[i]) { 
			
			if (j != 0) 
				j = lps[j - 1]; 
			else
				i = i + 1; 
		} 
	} 
} 


void computeLPSArray(char* pat, int M, int* lps) 
{ 
	
	int len = 0; 

	lps[0] = 0; // lps[0] is always 0 

	
	int i = 1; 
	while (i < M) { 
		if (pat[i] == pat[len]) { 
			len++; 
			lps[i] = len; 
			i++; 
		} 
		else 
		{ 
			
			if (len != 0) { 
				len = lps[len - 1]; 

			} 
			else 
			{ 
				lps[i] = 0; 
				i++; 
			} 
		} 
	} 
} 

int main() 
{ 
	char txt[] = "ABABDABACDABABCABAB"; 
	char pat[] = "ABABCABAB"; 
	KMPSearch(pat, txt); 
	return 0; 
}