Change project structure to a Maven Java project + Refactor (#2816)

src/main/java/com/thealgorithms/others/StringMatchFiniteAutomata.java

@@ -0,0 +1,85 @@
+package com.thealgorithms.others;
+
+/**
+ * @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;
+    }
+}