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Linear search

In the field of 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 i in array
       return true if i == value;
   return false

Here is a sample implementation in PHP:

function linear_search($array, $value)
   foreach ($array as $current) {
       if ($current == $value) {
           return TRUE;
   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.