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Others/StringMatchFiniteAutomata.java
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@ -1,91 +1,81 @@
/**
* @author Prateek Kumar Oraon (https://github.com/prateekKrOraon)
*/
/** @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);
// An implementaion of string matching using finite automata
public class StringMatchFiniteAutomata {
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;
}
}
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;
}
}