gno.land/r/moul/x/daily/stack/v0⧉

1// Package stack is an educational data-structure playground that keeps BOTH a2// LIFO stack and a FIFO queue of ints, so you can compare how the two behave.3package stack45import (6	"chain"7	"strconv"8	"strings"9)1011// stackData holds the LIFO stack; the last pushed element is the "top".12var stackData []int1314// queueData holds the FIFO queue; the oldest enqueued element is the "front".15var queueData []int1617// Push adds n to the top of the LIFO stack.18func Push(cur realm, n int) {19	stackData = append(stackData, n)20	chain.Emit("Push", "n", strconv.Itoa(n), "size", strconv.Itoa(len(stackData)))21}2223// Pop removes and returns the top element of the LIFO stack.24// It panics (a cross-realm abort) if the stack is empty.25func Pop(cur realm) int {26	if len(stackData) == 0 {27		panic("stack is empty: nothing to pop")28	}29	last := len(stackData) - 130	n := stackData[last]31	stackData = stackData[:last]32	chain.Emit("Pop", "n", strconv.Itoa(n), "size", strconv.Itoa(len(stackData)))33	return n34}3536// Enqueue adds n to the back of the FIFO queue.37func Enqueue(cur realm, n int) {38	queueData = append(queueData, n)39	chain.Emit("Enqueue", "n", strconv.Itoa(n), "size", strconv.Itoa(len(queueData)))40}4142// Dequeue removes and returns the front element of the FIFO queue.43// It panics (a cross-realm abort) if the queue is empty.44func Dequeue(cur realm) int {45	if len(queueData) == 0 {46		panic("queue is empty: nothing to dequeue")47	}48	n := queueData[0]49	queueData = queueData[1:]50	chain.Emit("Dequeue", "n", strconv.Itoa(n), "size", strconv.Itoa(len(queueData)))51	return n52}5354// StackSize returns the number of elements in the LIFO stack.55func StackSize() int { return len(stackData) }5657// QueueSize returns the number of elements in the FIFO queue.58func QueueSize() int { return len(queueData) }5960// renderInts formats a slice of ints as a space-separated list, e.g. "1 2 3".61func renderInts(xs []int) string {62	if len(xs) == 0 {63		return "_(empty)_"64	}65	parts := make([]string, len(xs))66	for i, x := range xs {67		parts[i] = strconv.Itoa(x)68	}69	return "`" + strings.Join(parts, " ") + "`"70}7172// Render returns a Markdown view of both structures with top/front labeled,73// their sizes, and a one-line explanation of LIFO vs FIFO.74func Render(path string) string {75	var b strings.Builder7677	b.WriteString("# Stack & Queue Playground\n\n")78	b.WriteString("A **stack** is LIFO (last in, first out) — the last item pushed is the first popped. ")79	b.WriteString("A **queue** is FIFO (first in, first out) — the first item enqueued is the first dequeued.\n\n")8081	b.WriteString("## Stack (LIFO) — size ")82	b.WriteString(strconv.Itoa(len(stackData)))83	b.WriteString("\n\n")84	b.WriteString("Contents (bottom → top): ")85	b.WriteString(renderInts(stackData))86	b.WriteString("\n\n")87	if len(stackData) > 0 {88		b.WriteString("Top: `")89		b.WriteString(strconv.Itoa(stackData[len(stackData)-1]))90		b.WriteString("` — the next `Pop` returns this.\n\n")91	} else {92		b.WriteString("Top: _(none)_ — `Pop` would panic.\n\n")93	}9495	b.WriteString("## Queue (FIFO) — size ")96	b.WriteString(strconv.Itoa(len(queueData)))97	b.WriteString("\n\n")98	b.WriteString("Contents (front → back): ")99	b.WriteString(renderInts(queueData))100	b.WriteString("\n\n")101	if len(queueData) > 0 {102		b.WriteString("Front: `")103		b.WriteString(strconv.Itoa(queueData[0]))104		b.WriteString("` — the next `Dequeue` returns this.\n\n")105	} else {106		b.WriteString("Front: _(none)_ — `Dequeue` would panic.\n\n")107	}108109	b.WriteString("---\n\n")110	b.WriteString("_Tip: push the same sequence into both, then Pop vs Dequeue to see LIFO reverse it while FIFO preserves order._\n")111112	return b.String()113}114