lautomata.cpp

#include <bits/stdc++.h>
using namespace std;
#define NO_OF_CHARS 256

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.length();
  int N = txt.length();

  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 t, p;
  cout << "Enter text : ";
  cin >> t;
  cout << "Enter pattern : ";
  cin >> p;

  search(p, t);
  return 0;
}