Stacks and Queues

Stack Push/Pop

Push values onto a stack and pop them back in last-in, first-out order.

Algorithm

The replay uses the same three values in every language, so this Lua DSA implementation can be compared directly with the rest of the DSA track.

Basic Implementation

basic.lua 
local function render(values)
    local parts = {}
    for i, value in ipairs(values) do parts[i] = tostring(value) end
    return table.concat(parts, " -> ")
end

local stack = {}
for _, value in ipairs({10, 20, 30}) do table.insert(stack, value) end
local popped = {}
while #stack > 0 do table.insert(popped, table.remove(stack)) end
print(render(popped))

Complexity

  • Time: O(1) per push/pop
  • Space: O(n)

Implementation notes

  • Keep the explicit stack/queue operations. Library shortcuts that only produce the final list hide the data-structure behavior this lesson is meant to replay.
  • The final output uses a deterministic a -> b -> c format for cross-language comparison.
top The top is the most recently pushed value.
LIFO A stack removes values in last-in, first-out order.