Linear search

Helping orphans the way you would do it

In computer science, linear search is a search algorithm, also known as sequential search, that is suitable for searching a set of data for a particular value.

It operates by checking every element of a list until a match is found. Linear search runs in O(N). If the data are distributed randomly, on average N/2 comparisons will be needed. The best case is that the value is equal to the first element tested, in which case only 1 comparison is needed. The worst case is that the value is not in the list, in which case N comparisons are needed.

Here is a sample implementation in Ruby:

def linear_search(array, value)
   for element in array

       return true if element == value

   end

   return false

end

Here is a sample implementation in PHP:

function linear_search($array, $value)
{
   foreach ($array as $current) {

       if ($current == $value) {

           return TRUE;

       }

   }

   return FALSE;

}

And here is a sample implementation in C++ using templates and STL containers:

template 
bool linear_search(const C& array, const T& value) {
   C::const_iterator iter = array.begin();

   C::const_iterator end = array.end();

   while (iter != end) {

       if (*iter == value)

           return true;

       ++iter;

   }

   return false;

}

Linear search can be used to search an unordered list. The more efficient binary search can only be used to search an ordered list.

If more than a small number of searches are needed, it is advisable to use a more efficient data structure. One approach is to sort and then use binary searches. Another common one is to build up a hash table and then do hash lookups.