Stacks, Queues & Two Pointers

A slice is already a stack and a queue

You don't import a stack in Go — a slice is one. A stack is LIFO (last in, first out), like an undo history: the last thing you did is the first you undo.

• Push: stack = append(stack, x) — O(1) amortized.

• Peek: stack[len(stack)-1] — the top.

• Pop: stack = stack[:len(stack)-1] — reslice to drop the last element, O(1).

A queue is FIFO (first in, first out), like a job queue. Enqueue with append; dequeue from the front with queue = queue[1:]. (Reslicing the front is fine for interview-sized inputs; a production hot loop would use a ring buffer or container/list to avoid the underlying array growing forever.)