Python · Theory

Stack & Queue

Theory

96/268

Stack & Queue

Stack = LIFO. Use a list: append + pop(). Queue = FIFO. Use collections.deque: append + popleft() (list pop(0) is slow).

Board — stack [1,2,3] pop → 3. Queue Asha,Ravi popleft → Asha first.

Stack & Queue — output — stack pop B (LIFO) then queue Asha (FIFO).

Exam tip

LIFO vs FIFO + which Python type.

Example

# Stack & Queue
from collections import deque
stack = []
stack.append("A")
stack.append("B")
print("stack pop", stack.pop())
q = deque(["Asha", "Ravi"])
print("queue", q.popleft())

Stack & Queue — output: stack pop B (LIFO) then queue Asha (FIFO).

Short notes

Stack LIFO : append/pop
Queue FIFO : deque popleft
Traplist.pop(0) is O(n)

Python · Theory

Stack & Queue

← All stacks

Theory

96/268

Stack & Queue

Stack = LIFO. Use a list: append + pop(). Queue = FIFO. Use collections.deque: append + popleft() (list pop(0) is slow).

Board — stack [1,2,3] pop → 3. Queue Asha,Ravi popleft → Asha first.

Stack & Queue — output — stack pop B (LIFO) then queue Asha (FIFO).

Exam tip

LIFO vs FIFO + which Python type.

Example

# Stack & Queue
from collections import deque
stack = []
stack.append("A")
stack.append("B")
print("stack pop", stack.pop())
q = deque(["Asha", "Ravi"])
print("queue", q.popleft())

Stack & Queue — output: stack pop B (LIFO) then queue Asha (FIFO).

Short notes

Stack LIFO : append/pop
Queue FIFO : deque popleft
Traplist.pop(0) is O(n)

Stack & Queue

Example

Short notes

Questions

Stack & Queue

Example

Short notes

Questions