From afe6c313cb1a7e4dc8c6becc96c193089b63c930 Mon Sep 17 00:00:00 2001
From: Henrik Christensen <sensen1695@hotmail.com>
Date: Mon, 1 Nov 2021 12:35:06 +0100
Subject: [PATCH] implemented stack and queue in Go

---
 .../stacks_and_queues/code/go/stack-queue.go  | 138 ++++++++++++++++++
 .../stacks_and_queues/stacks_and_queues.md    |   4 +
 2 files changed, 142 insertions(+)
 create mode 100644 contents/stacks_and_queues/code/go/stack-queue.go

diff --git a/contents/stacks_and_queues/code/go/stack-queue.go b/contents/stacks_and_queues/code/go/stack-queue.go
new file mode 100644
index 000000000..260919e01
--- /dev/null
+++ b/contents/stacks_and_queues/code/go/stack-queue.go
@@ -0,0 +1,138 @@
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+type stackNode struct {
+	value interface{}
+	prev  *stackNode
+}
+
+type Stack struct {
+	top    *stackNode
+	length int
+}
+
+// NewStack initializes a new stack.
+func NewStack() *Stack {
+	return &Stack{top: nil, length: 0}
+}
+
+// Push adds an element to the stack and returns the length of the stack.
+func (s *Stack) Push(v interface{}) int {
+	n := &stackNode{value: v, prev: s.top}
+	s.top = n
+	s.length++
+	return s.length
+}
+
+// Pop removes and returns the last item from the stack.
+func (s *Stack) Pop() interface{} {
+	if s.length == 0 {
+		fmt.Fprint(os.Stderr, "cannot pop items of an empty stack")
+		os.Exit(1)
+	}
+	item := s.top
+	s.top = item.prev
+	s.length--
+	return item.value
+}
+
+// Size returns the size of the stack.
+func (s Stack) Size() int {
+	return s.length
+}
+
+// Top returns the last item in the stack.
+func (s Stack) Top() interface{} {
+	if s.length == 0 {
+		fmt.Fprint(os.Stderr, "cannot peek an empty stack")
+		os.Exit(1)
+	}
+	return s.top.value
+}
+
+type queueNode struct {
+	value interface{}
+	next  *queueNode
+}
+
+type Queue struct {
+	front  *queueNode
+	length int
+}
+
+// NewQueue initializes a new queue.
+func NewQueue() *Queue {
+	return &Queue{front: nil, length: 0}
+}
+
+// Enqueue adds an item to the queue and returns the length of the queue.
+func (q *Queue) Enqueue(v interface{}) int {
+	n := &queueNode{value: v, next: nil}
+	if q.front == nil {
+		q.front = n
+	} else {
+		last := q.front
+		for last.next != nil {
+			last = last.next
+		}
+		last.next = n
+	}
+	q.length++
+	return q.length
+}
+
+// Dequeue removes and returns an item from the queue.
+func (q *Queue) Dequeue() interface{} {
+	if q.length == 0 {
+		fmt.Fprint(os.Stderr, "cannot dequeue an empty queue")
+		os.Exit(1)
+	}
+	item := q.front
+	if q.length == 1 {
+		q.front = nil
+	} else {
+		q.front = q.front.next
+	}
+	q.length--
+	return item.value
+}
+
+// Size returns the size of the queue.
+func (q Queue) Size() int {
+	return q.length
+}
+
+// Front returns the first element in the queue.
+func (q Queue) Front() interface{} {
+	if q.length == 0 {
+		fmt.Fprint(os.Stderr, "cannot peek an empty queue")
+		os.Exit(1)
+	}
+	return q.front.value
+}
+
+func main() {
+	stack := NewStack()
+
+	stack.Push(4)
+	stack.Push(5)
+	stack.Push(9)
+
+	fmt.Println(stack.Pop())
+	fmt.Println(stack.Size())
+	fmt.Println(stack.Top())
+
+	queue := NewQueue()
+
+	queue.Enqueue(4)
+	queue.Enqueue(5)
+	queue.Enqueue(9)
+
+	fmt.Println(queue.Dequeue())
+	fmt.Println(queue.Size())
+	fmt.Println(queue.Front())
+}
diff --git a/contents/stacks_and_queues/stacks_and_queues.md b/contents/stacks_and_queues/stacks_and_queues.md
index 89a77be9a..57c16e4d2 100644
--- a/contents/stacks_and_queues/stacks_and_queues.md
+++ b/contents/stacks_and_queues/stacks_and_queues.md
@@ -20,6 +20,8 @@ Here is a simple implementation of a stack:
 [import, lang:"typescript"](code/typescript/stack.ts)
 {% sample lang="java" %}
 [import, lang:"java"](code/java/Stack.java)
+{% sample lang="go" %}
+[import:8-55, lang:"go"](code/go/stack-queue.go)
 {% endmethod %}
 
 Here is a simple implementation of a queue:
@@ -28,6 +30,8 @@ Here is a simple implementation of a queue:
 [import, lang:"typescript"](code/typescript/queue.ts)
 {% sample lang="java" %}
 [import, lang:"java" ](code/java/Queue.java)
+{% sample lang="go" %}
+[import:57-116, lang:"go"](code/go/stack-queue.go)
 {% endmethod %}