From 6f9dc7b91ba5c5022438b9d6872cc458e993aa2f Mon Sep 17 00:00:00 2001
From: Gregory <neogen570@gmail.com>
Date: Mon, 8 Nov 2021 20:32:55 +0200
Subject: [PATCH] init

---
 fundamentals/stack/stack.go      | 50 ++++++++++++++++++++++++++++++++
 fundamentals/stack/stack_test.go | 34 ++++++++++++++++++++++
 go.mod                           |  3 ++
 3 files changed, 87 insertions(+)
 create mode 100644 fundamentals/stack/stack.go
 create mode 100644 fundamentals/stack/stack_test.go
 create mode 100644 go.mod

diff --git a/fundamentals/stack/stack.go b/fundamentals/stack/stack.go
new file mode 100644
index 0000000..d94296e
--- /dev/null
+++ b/fundamentals/stack/stack.go
@@ -0,0 +1,50 @@
+package stack
+
+// "Generic" item.
+// When type parameters will land this type became
+// type Item[T any] T
+type Item interface{}
+
+type Stack interface {
+	Push(Item)
+	Pop() Item
+	Size() int
+	IsEmpty() bool
+}
+
+// We use linked list as internal data structure
+// to get O(1) speed for push and pop opeartions
+type node struct {
+	item Item
+	next *node
+}
+
+type stack struct {
+	size int
+	head *node
+}
+
+func NewStack() Stack {
+	return &stack{}
+}
+
+func (s *stack) Push(item Item) {
+	next := s.head
+	s.head = &node{item, next}
+	s.size++
+}
+
+func (s *stack) Pop() Item {
+	head := s.head
+	s.head = head.next
+	s.size--
+	return head.item
+}
+
+func (s *stack) Size() int {
+	return s.size
+}
+
+func (s *stack) IsEmpty() bool {
+	return s.size == 0
+}
diff --git a/fundamentals/stack/stack_test.go b/fundamentals/stack/stack_test.go
new file mode 100644
index 0000000..d7c443a
--- /dev/null
+++ b/fundamentals/stack/stack_test.go
@@ -0,0 +1,34 @@
+package stack
+
+import (
+	"log"
+	"testing"
+)
+
+func TestSimple(t *testing.T) {
+	stack := NewStack()
+
+	stack.Push(1)
+	stack.Push(2)
+
+	if stack.Pop().(int) != 2 {
+		log.Fatal("wrong stack value")
+	}
+}
+
+func TestSize(t *testing.T) {
+	stack := NewStack()
+
+	if !stack.IsEmpty() {
+		log.Fatal("should be empty")
+	}
+
+	stack.Push(1)
+	stack.Push(2)
+	stack.Push(3)
+
+	if stack.Size() != 3 {
+		log.Fatal("wrong size")
+	}
+
+}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..44584f2
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module github.com/fotonmoton/algorithms
+
+go 1.16