🥞 Stack & Queue — LIFO vs FIFO

Push values, then pop the stack top or dequeue the queue front.

💡 Same values go into both. Click the stack top or queue front to remove — or try a middle node to learn the rule.

Value to push

Output order

stack (LIFO)—

queue (FIFO)—

Same inputs, opposite output order — the stack reverses, the queue preserves.

Operations · O(1) each

1Stack (LIFO)
2  push(v):  node.next → top;  top ← node
3  pop():    v ← top;  top ← top.next;  return v
4Queue (FIFO)
5  enqueue(v):  tail.next → node;  tail ← node
6  dequeue():   v ← head;  head ← head.next;  return v

Stack vs Queue Visualizer: LIFO and FIFO Side by Side

This lab runs a stack and a queue side by side on the identical stream of pushes, so the difference between last-in-first-out and first-in-first-out becomes something you can see rather than memorize. Each structure is drawn as a linked list with next-pointer arrows, a TOP marker on the stack and a FRONT marker on the queue, and an output tape that records the order values leave. Pop the stack and the newest value exits; dequeue the queue and the oldest does — empty both after the same pushes and the stack's output is the exact reverse of the queue's. It's hands-on: click the top or front node to remove it, or click a middle node to learn why you can't, since both structures expose exactly one end for O(1) access.

What you can do in this simulation

Push a value and it enters both structures at once; pop the stack top or dequeue the queue front and watch the outputs diverge
Click a node to remove it — the lab allows only the stack's top or the queue's front and explains the LIFO/FIFO rule when you try a middle node
Output tapes record the order values leave, making 'same input, reversed output' obvious
Animated next-pointer arrows and TOP / FRONT markers show the linked-list structure and O(1) access
Run the reverse demo, clear the board, and complete missions covering LIFO, FIFO, and the one-end access rule

Concepts covered

stack data structure · queue data structure · LIFO · FIFO · linked list · push pop enqueue dequeue · O(1) operations

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1Stack (LIFO)

2 push(v): node.next → top; top ← node

3 pop(): v ← top; top ← top.next; return v

4Queue (FIFO)

5 enqueue(v): tail.next → node; tail ← node

6 dequeue(): v ← head; head ← head.next; return v

Stack vs Queue Visualizer: LIFO and FIFO Side by Side

What you can do in this simulation

Push a value and it enters both structures at once; pop the stack top or dequeue the queue front and watch the outputs diverge

Click a node to remove it — the lab allows only the stack's top or the queue's front and explains the LIFO/FIFO rule when you try a middle node

Output tapes record the order values leave, making 'same input, reversed output' obvious

Animated next-pointer arrows and TOP / FRONT markers show the linked-list structure and O(1) access

Run the reverse demo, clear the board, and complete missions covering LIFO, FIFO, and the one-end access rule