Stacks And Queues Comparison

Main Rule

Structure	Rule
Stack	Last In, First Out
Queue	First In, First Out
Priority Queue	Highest priority first

Operation Comparison

Structure	Insert	Delete	Peek
Stack	`push` at top	`pop` from top	top element
Simple Queue	`enqueue` at rear	`dequeue` from front	front element
Circular Queue	`enqueue` at rear with wrap-around	`dequeue` from front with wrap-around	front element
Priority Queue	insert by priority rule	remove highest-priority item	highest-priority item

Time Complexity Table

Structure	Insert	Delete	Peek
Stack	`O(1)`	`O(1)`	`O(1)`
Simple Queue	`O(1)`	`O(1)`	`O(1)`
Circular Queue	`O(1)`	`O(1)`	`O(1)`
Priority Queue (unsorted array)	`O(1)`	`O(n)`	`O(n)`
Priority Queue (heap)	`O(log n)`	`O(log n)`	`O(1)`

When To Use What

Choose Stack if:

last inserted item should come out first
you are dealing with recursion, undo, brackets, or expressions

Choose Simple Queue if:

first entered item should leave first
array waste is not a problem

Choose Circular Queue if:

you want efficient reuse of array space

Choose Priority Queue if:

some items must be handled before others