Linear Search in Sorted Lists

linear_search.php

<?php
  /**
   * Performs a sequential search using sentinel
   * and changes the array after the value is found
   *
   * @param array $arr
   * @param mixed $value
   */
  function sequential_search(&$arr, $value)
  {
  	$arr[] = $value;
  	$index = 0;
   
  	while ($arr[$index++] != $value);
   
  	if ($index < count($arr)) {
   
  		// put the item at the front of the list
  		array_unshift($arr, $arr[$index-1]);
   
  		// remove the value from its previous position
  		unset($arr[$index]);
   
  		// unset the sentinel
  		unset($arr[count($arr)+1]);
   
  		return true;
  	}
   
  	return false;
  }
   
  // the list
  $arr = array(1, 2, 3, 3.14, 5, 4, 6, 9, 8);
   
  // the value
  $x = 3.14;
   
  if (sequential_search($arr, $x)) {
  	// now the array is changed to
  	// (3.14, 1, 2, 3, 5, 4, 6, 9, 8)
  	echo "The value $x is found!";
  } else {
  	echo "The value $x doesn't appear to be in the list!";
  }
?>

linear_search_v1.php

<?php
  // list with username/name pairs
  $arr = array(
  	array('name' => 'James Bond', 'username' => 'jamesbond007'),
  	array('name' => 'John Smith', 'username' => 'jsmith'),
  	array('name' => 'John Silver', 'username' => 'hohoho'),
  	array('name' => 'Yoda', 'username' => 'masteryoda900'),
  	array('name' => 'Darth Vader', 'username' => 'vader'),
  );
  
  /**
   * Performs a sequential search using a sentinel.
   * Returns the index of the item if the item was found
   * and FALSE otherwise.
   * 
   * @param array $arr
   * @param mixed $value
   */
  function sequential_search(&$arr, $value)
  {	
  	// usign a sentinel
  	$arr[] = array('username' => $value, 'name' => '');
  	$index = 0;
   
  	while ($arr[$index++]['username'] != $value);
   
  	// if the desired element is in the array
  	if ($index < count($arr)) {
   
  		// push the element at the front of the list
  		array_unshift($arr, $arr[$index-1]);
   
  		// remove the item from its previous place
  		unset($arr[$index]);
   
  		// remove the sentinel
  		unset($arr[count($arr)]);
   
  		// return the index of the value
  		return $index;
  	}
   
  	// the element has not been found
  	return FALSE;
  }
   
  if (FALSE !== ($iterations = sequential_search($arr, 'vader'))) {
  	echo "Hello, {$arr[0]['name']}";
  	echo "Found after $iterations iterations!";
  } else {
  	echo "Hi, guest!";
  }
   
  if (FALSE !== ($iterations = sequential_search($arr, 'vader'))) {
  	echo "Hello, {$arr[0]['name']}";
  	echo "Found after $iterations iterations!";
  } else {
  	echo "Hi, guest!";
  }
?>