Stack (LIFO)
Applies to: general
A stack is a last-in, first-out (LIFO) collection: you push onto the top and pop from the top. It models
nested structure, function calls use the call stack, and it powers depth-first traversal and expression
evaluation.
push 1, push 2, push 3 -> top is 3
pop -> 3, pop -> 2 -> LIFO order