<?php
session_start();

if ( ! $_SESSION['game'] )
{

  $file_with_city = 'city.txt';
  $main = file ( $file_with_city );

  foreach ( $main as $city )
  {
    $city = trim ( $city );
    if ( strlen ( $city ) < 2 )
      continue;

    $first_symb = substr ( $city, 0, 1 );
    $city_array[$first_symb][] = $city;

  }

  $_SESSION['city'] = $city_array;
  echo "<pre>";
  print_r($_SESSION['city']);
  echo "</pre>";
  $_SESSION['game'] = 1;
  $_SESSION['last_symb'] = "а";
  
}

if ( $_POST['text'] != '' )
{

  echo "Вы ввели Город {$_POST['text']}.<br />";
  $first_symb = substr ( $_POST['text'], 0, 1 );

  if ( $first_symb != $_SESSION['last_symb'] )
  {
    echo "Вы должны ввести город на букву <b>{$_SESSION['last_symb']}</b><br />";
  }
  else
  {

    if ( !isset ( $_SESSION['city'][$first_symb] ) or ! @in_array ( $_POST['text'], $_SESSION['city'][$first_symb] ) )
    {
      echo "Такого города не существует.";
    }
    else
    {
      
      $delete_key = array_search ( $_POST['text'], $_SESSION['city'][$first_symb] );
      unset ( $_SESSION['city'][$first_symb][$delete_key] );

      $last_symb = substr ( $_POST['text'], -1 );
      $_SESSION['last_symb'] = $last_symb;

      $answer_count = count ( $_SESSION['city'][$last_symb] );

      if ( $answer_count == 0 )
      {
        session_unset();
        die ( "Вы победили!" );
      }
      else
      {
      
        $rand = rand ( 0, $answer_count - 1 );
        $answer = $_SESSION['city'][$last_symb][$rand];
        unset ( $_SESSION['city'][$last_symb][$rand] );
        echo "Компьютер отвечает: <b>$answer</b><br />";
        $ls = substr ( $answer, -1 );
        $_SESSION['last_symb'] = $ls;
        
        if ( count ( $_SESSION['city'][$ls] ) < 1 )
        { 
          session_unset();
          die ( "Вы проиграли!" );
        }

      }
      
    }
    
  }
  
}

echo "<form action='' method='post'>
Введите Город:
<input type='text' name='text' value='' />
<input type='submit' name='submit' value='submit' />
</form>";

?>