Finite Automata algorithm for Pattern Searching | CPP program for Finite Automata Pattern searching Algorithm ; If the character c is same as next character in pattern , then simply increment state ; ns stores the result which is next state ; Start from the largest possible value and stop when you find a prefix which is also suffix ; This function builds the TF table which represents4 Finite Automata for a given pattern ; Prints all occurrences of pat in txt ; Process txt over FA . ; Driver program to test above function
#include <bits/stdc++.h> NEW_LINE using namespace std ; #define NO_OF_CHARS  256 NEW_LINE int getNextState ( string pat , int M , int state , int x ) { if ( state < M && x == pat [ state ] ) return state + 1 ; int ns , i ; for ( ns = state ; ns > 0 ; ns -- ) { if ( pat [ ns - 1 ] == x ) { for ( i = 0 ; i < ns - 1 ; i ++ ) if ( pat [ i ] != pat [ state - ns + 1 + i ] ) break ; if ( i == ns - 1 ) return ns ; } } return 0 ; } void computeTF ( string pat , int M , int TF [ ] [ NO_OF_CHARS ] ) { int state , x ; for ( state = 0 ; state <= M ; ++ state ) for ( x = 0 ; x < NO_OF_CHARS ; ++ x ) TF [ state ] [ x ] = getNextState ( pat , M , state , x ) ; } void search ( string pat , string txt ) { int M = pat . size ( ) ; int N = txt . size ( ) ; int TF [ M + 1 ] [ NO_OF_CHARS ] ; computeTF ( pat , M , TF ) ; int i , state = 0 ; for ( i = 0 ; i < N ; i ++ ) { state = TF [ state ] [ txt [ i ] ] ; if ( state == M ) cout << " ▁ Pattern ▁ found ▁ at ▁ index ▁ " << i - M + 1 << endl ; } } int main ( ) { string txt = " AABAACAADAABAAABAA " ; string pat = " AABA " ; search ( pat , txt ) ; return 0 ; }