91 lines
1.7 KiB
Java
91 lines
1.7 KiB
Java
/**
|
|
* @author Prateek Kumar Oraon (https://github.com/prateekKrOraon)
|
|
*/
|
|
import java.util.Scanner;
|
|
|
|
//An implementaion of string matching using finite automata
|
|
public class StringMatchFiniteAutomata{
|
|
|
|
public static final int CHARS = 256;
|
|
public static int[][] FA;
|
|
public static Scanner scanner = null;
|
|
|
|
public static void main(String[] args){
|
|
|
|
scanner = new Scanner(System.in);
|
|
System.out.println("Enter String");
|
|
String text = scanner.nextLine();
|
|
System.out.println("Enter pattern");
|
|
String pat = scanner.nextLine();
|
|
|
|
searchPat(text, pat);
|
|
|
|
scanner.close();
|
|
|
|
}
|
|
|
|
public static void searchPat(String text, String pat){
|
|
|
|
int m = pat.length();
|
|
int n = text.length();
|
|
|
|
FA = new int[m+1][CHARS];
|
|
|
|
computeFA(pat, m ,FA);
|
|
|
|
int state = 0;
|
|
for(int i=0;i<n;i++){
|
|
state = FA[state][text.charAt(i)];
|
|
|
|
if(state == m){
|
|
System.out.println("Pattern found at index " + (i-m+1));
|
|
}
|
|
}
|
|
|
|
}
|
|
|
|
//Computes finite automata for the partern
|
|
public static void computeFA(String pat, int m, int[][] FA){
|
|
|
|
for(int state = 0; state<= m; ++state){
|
|
for(int x =0; x< CHARS; ++x){
|
|
FA[state][x] = getNextState(pat, m, state, x);
|
|
}
|
|
}
|
|
|
|
}
|
|
|
|
public static int getNextState(String pat, int m, int state, int x){
|
|
|
|
//if current state is less than length of pattern
|
|
//and input character of pattern matches the character in the alphabet
|
|
//then automata goes to next state
|
|
if(state < m && x==pat.charAt(state)){
|
|
return state+1;
|
|
}
|
|
|
|
for(int ns = state; ns>0; ns--){
|
|
|
|
if(pat.charAt(ns-1) == x){
|
|
|
|
for(int i=0; i<ns-1; i++){
|
|
|
|
if(pat.charAt(i) != pat.charAt(state-ns+i+1)){
|
|
break;
|
|
}
|
|
|
|
if(i == ns-1){
|
|
return ns;
|
|
}
|
|
|
|
}
|
|
|
|
}
|
|
|
|
}
|
|
|
|
return 0;
|
|
|
|
}
|
|
|
|
} |