programming-for-dummies

370
Using Deques
The second Contains command looks for the “Orange juice” string.
Because this string isn’t stored in the stack, this Contains command
returns a False value, which is stored in the Y variable.
The Contains command just tells you whether a chunk of data is in a
queue, but it doesn’t tell you where in the queue that data might be.
Using Deques
A queue only lets you add data on one end of the data structure and remove
data from the opposite end. A deque (pronounced deck) acts like a queue
that lets you add or remove data from either end, as shown in Figure 4-7.
A deque allows you to add or remove data
from both ends of the data structure.
Figure 4-7:
A deque
acts like a
two-way
queue.
New data
1 2
Data #4 Data #3
3 4
Data #2 Data #1 New data
Most programming languages don’t offer the deque data structure as a builtin
feature. Instead, you have to create a queue with other data structures,
such as a linked list, and then write code to manage the storage and removal
of data from both ends of the deque.
A deque is basically a linked list of nodes that contain data and two pointers:
✦ One pointer points to the previous node.
✦ The second pointer points to the next node, as shown in Figure 4-8.
Figure 4-8:
Each node
in a deque
contains two
pointers that
point to the
next and previous
node.
A double-linked list consists of nodes that hold data and two
pointers that point to the next and previous nose.
Data Data Data Data