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;
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;
}
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.