
Data Structure

This illustrates a data structure, a means of storing data within a program.

You may see other such structures in the Data Structures category.
 Illustration of FIFO behavior
Task

Implement a FIFO queue.

Elements are added at one side and popped from the other in the order of insertion.



Operations:

   push   (aka enqueue)    - add element
   pop     (aka dequeue)    - pop first element
   empty                             - return truth value when empty


Errors:

   handle the error of trying to pop from an empty queue (behavior depends on the language and platform)


See

   Queue/Usage   for the built-in FIFO or queue of your language or standard library.


See also

 Array
 Associative array: Creation, Iteration
 Collections
 Compound data type
 Doubly-linked list: Definition, Element definition, Element insertion, List Traversal, Element Removal
 Linked list
 Queue: Definition, Usage
 Set
 Singly-linked list: Element definition, Element insertion, List Traversal, Element Removal
 Stack


Queue = {}
 
function Queue.new()
    return { first = 0, last = -1 }
end
 
function Queue.push( queue, value )
    queue.last = queue.last + 1
    queue[queue.last] = value
end
 
function Queue.pop( queue )
    if queue.first > queue.last then
        return nil
    end
 
    local val = queue[queue.first]
    queue[queue.first] = nil
    queue.first = queue.first + 1
    return val
end
 
function Queue.empty( queue )
    return queue.first > queue.last
end