master-algorithms-py

last in, first out structures (LIFO)
useful in certain recursive algorithms, where you can push temp data as you recurse, and remove them from the (memory or data structure) stack as you backtrace.

queues

first in, first out structures (FIFO), i.e., items are removed at the same order they are added.
queues can be implemented with two arrays or a dynamic array (linked list), as long as items are added and removed from opposite sides.
if implemented with a dynamic array, a more efficient solution is to use a circular queue (ring buffer), i.e. a fixed-size array and two pointers to indicate the starting and ending positions. an advantage of circular queues is that we can use the spaces in front of the queue. in a normal queue, once the queue becomes full, we cannot insert the next element even if there is a space in front of the queue. but using the circular queue, we can use the space to store new values.
queues are often used in breath-first search (where you store a list of nodes to be processed) or when implementing a cache.

`Queues.py`

> python3 queues.py

🧪 Testing Queue...
Is the queue empty? True
Adding 1 to 10 in the queue...
Queue: [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]

Queue size: 10
Queue peek : 1
Is the queue empty? False

Dequeue...
Queue: [10, 9, 8, 7, 6, 5, 4, 3, 2]

Queue size: 9
Queue peek: 2
Is the queue empty? False


🧪 Testing Priority Queue...
Priority Queue: [(-4, 1, Item 4), (-1, 0, Item 1), (-3, 2, Item 3)]
Pop: Item 4
Priority Queue: [(-3, 2, Item 3), (-1, 0, Item 1)]

`stack.py`

python3 stack.py

Testing Stack...

Stack: [12, 13, 14, 15, 16, 17, 18, 19, 20]
Stack size: 9
Stack peek: 20
Stack is empty: False
Stack min: 12

Popping...
20
19
18
17
16
Stack: [12, 13, 14, 15]