From d7f6343df1e79392e95f13b99956d5ab960a47d0 Mon Sep 17 00:00:00 2001
From: blindlobstar <boryapictures@gmail.com>
Date: Tue, 8 Apr 2025 02:13:54 +0200
Subject: [PATCH] concurrent queue iii problem

---
 12-concurrent-queue-iii/README.md            |  11 ++
 12-concurrent-queue-iii/solution/solution.go |  58 +++++++
 12-concurrent-queue-iii/task.go              |  25 +++
 12-concurrent-queue-iii/task_test.go         | 163 +++++++++++++++++++
 README.md                                    |   1 +
 5 files changed, 258 insertions(+)
 create mode 100644 12-concurrent-queue-iii/README.md
 create mode 100644 12-concurrent-queue-iii/solution/solution.go
 create mode 100644 12-concurrent-queue-iii/task.go
 create mode 100644 12-concurrent-queue-iii/task_test.go

diff --git a/12-concurrent-queue-iii/README.md b/12-concurrent-queue-iii/README.md
new file mode 100644
index 0000000..ea6c91a
--- /dev/null
+++ b/12-concurrent-queue-iii/README.md
@@ -0,0 +1,11 @@
+# Concurrent Queue
+Implement a thread-safe **zero allocation** queue with the following properties:
+
+- It has a fixed maximum size set at initialization.
+- `Push(val int) error` adds an item to the queue. If the queue is full, it should return `ErrQueueFull`.
+- `Pop() int` removes and returns first item from the queue. If the queue is empty, return -1.
+- `Peek() int` returns first item from the queue. If the queue is empty, return -1.
+- The queue must be safe to use from multiple goroutines simultaneously.
+
+## Tags
+`Concurrency`
diff --git a/12-concurrent-queue-iii/solution/solution.go b/12-concurrent-queue-iii/solution/solution.go
new file mode 100644
index 0000000..0ef73b4
--- /dev/null
+++ b/12-concurrent-queue-iii/solution/solution.go
@@ -0,0 +1,58 @@
+package main
+
+import (
+	"errors"
+	"sync"
+)
+
+var ErrQueueFull = errors.New("queue is full")
+
+type Queue struct {
+	data []int
+	w    int
+	r    int
+	sync.Mutex
+}
+
+func NewQueue(size int) *Queue {
+	return &Queue{
+		data: make([]int, size),
+	}
+}
+
+func (q *Queue) Push(val int) error {
+	q.Lock()
+	defer q.Unlock()
+
+	if q.w == q.r || q.w%len(q.data) != q.r%len(q.data) {
+		q.data[q.w%len(q.data)] = val
+		q.w++
+		return nil
+	} else {
+		return ErrQueueFull
+	}
+}
+
+func (q *Queue) Pop() int {
+	q.Lock()
+	defer q.Unlock()
+
+	if q.r != q.w {
+		val := q.data[q.r%len(q.data)]
+		q.r++
+		return val
+	} else {
+		return -1
+	}
+}
+
+func (q *Queue) Peek() int {
+	q.Lock()
+	defer q.Unlock()
+
+	if q.r != q.w {
+		return q.data[q.r%len(q.data)]
+	} else {
+		return -1
+	}
+}
diff --git a/12-concurrent-queue-iii/task.go b/12-concurrent-queue-iii/task.go
new file mode 100644
index 0000000..498208a
--- /dev/null
+++ b/12-concurrent-queue-iii/task.go
@@ -0,0 +1,25 @@
+package main
+
+import (
+	"errors"
+)
+
+var ErrQueueFull = errors.New("queue is full")
+
+type Queue struct{}
+
+func NewQueue(size int) *Queue {
+	return &Queue{}
+}
+
+func (q *Queue) Push(val int) error {
+	return nil
+}
+
+func (q *Queue) Pop() int {
+	return -1
+}
+
+func (q *Queue) Peek() int {
+	return -1
+}
diff --git a/12-concurrent-queue-iii/task_test.go b/12-concurrent-queue-iii/task_test.go
new file mode 100644
index 0000000..0659dd5
--- /dev/null
+++ b/12-concurrent-queue-iii/task_test.go
@@ -0,0 +1,163 @@
+package main
+
+import (
+	"context"
+	"reflect"
+	"sort"
+	"sync"
+	"testing"
+	"time"
+)
+
+func TestQueue(t *testing.T) {
+	tests := []struct {
+		name     string
+		size     int
+		ops      []string
+		args     []int
+		expected []any
+	}{
+		{
+			name:     "basic operations",
+			size:     3,
+			ops:      []string{"push", "push", "push", "pop", "pop", "pop"},
+			args:     []int{1, 2, 3, 0, 0, 0},
+			expected: []any{nil, nil, nil, 1, 2, 3},
+		},
+		{
+			name:     "empty queue pop",
+			size:     1,
+			ops:      []string{"pop", "push", "pop"},
+			args:     []int{0, 5, 0},
+			expected: []any{-1, nil, 5},
+		},
+		{
+			name:     "queue full error",
+			size:     2,
+			ops:      []string{"push", "push", "push", "pop", "push", "pop"},
+			args:     []int{5, 10, 15, 0, 20, 0},
+			expected: []any{nil, nil, ErrQueueFull, 5, nil, 10},
+		},
+		{
+			name:     "interleaved operations",
+			size:     2,
+			ops:      []string{"push", "pop", "push", "push", "pop", "pop"},
+			args:     []int{1, 0, 2, 3, 0, 0},
+			expected: []any{nil, 1, nil, nil, 2, 3},
+		},
+		{
+			name:     "peek operations",
+			size:     3,
+			ops:      []string{"push", "peek", "push", "peek", "pop", "peek", "pop", "peek"},
+			args:     []int{10, 0, 20, 0, 0, 0, 0, 0},
+			expected: []any{nil, 10, nil, 10, 10, 20, 20, -1},
+		},
+		{
+			name:     "peek empty queue",
+			size:     2,
+			ops:      []string{"peek", "push", "peek", "pop", "peek"},
+			args:     []int{0, 42, 0, 0, 0},
+			expected: []any{-1, nil, 42, 42, -1},
+		},
+		{
+			name:     "mixed operations",
+			size:     5,
+			ops:      []string{"push", "push", "peek", "pop", "peek", "push", "push", "push", "peek"},
+			args:     []int{5, 10, 0, 0, 0, 15, 20, 25, 0},
+			expected: []any{nil, nil, 5, 5, 10, nil, nil, nil, 10},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			q := NewQueue(tt.size)
+			results := make([]any, len(tt.ops))
+
+			for i, op := range tt.ops {
+				var result any
+
+				switch op {
+				case "push":
+					result = q.Push(tt.args[i])
+				case "pop":
+					result = q.Pop()
+				case "peek":
+					result = q.Peek()
+				}
+
+				results[i] = result
+			}
+
+			if !reflect.DeepEqual(results, tt.expected) {
+				t.Errorf("Expected: %v, got: %v", tt.expected, results)
+			}
+		})
+	}
+}
+
+func TestConcurrentQueue(t *testing.T) {
+	queue := NewQueue(1000)
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	var wg sync.WaitGroup
+	wg.Add(1000)
+	for i := range 1000 {
+		go func() {
+			defer wg.Done()
+			queue.Push(i + 1)
+		}()
+	}
+
+	ch := make(chan int, 1000)
+	go func() {
+		defer close(ch)
+		for {
+			select {
+			case <-ctx.Done():
+				return
+			default:
+				if val := queue.Pop(); val > -1 {
+					ch <- val
+				}
+			}
+		}
+	}()
+
+	go func() {
+		wg.Wait()
+		time.Sleep(100 * time.Millisecond)
+		cancel()
+	}()
+
+	var result []int
+	for val := range ch {
+		result = append(result, val)
+	}
+
+	expected := make([]int, 1000)
+	for i := range 1000 {
+		expected[i] = i + 1
+	}
+
+	sort.Ints(result)
+	if !reflect.DeepEqual(result, expected) {
+		t.Errorf("Expected: 1..1000, got: %v", result)
+	}
+}
+
+func TestQueueAllocations(t *testing.T) {
+	res := testing.Benchmark(BenchmarkQueue)
+	if res.AllocsPerOp() != 0 {
+		t.Errorf("Expected 0 allocation, got: %d", res.AllocsPerOp())
+	}
+}
+
+func BenchmarkQueue(b *testing.B) {
+	queue := NewQueue(1)
+	for b.Loop() {
+		queue.Push(1)
+		queue.Peek()
+		queue.Pop()
+	}
+}
diff --git a/README.md b/README.md
index 485b5d3..0cc7fe5 100644
--- a/README.md
+++ b/README.md
@@ -29,6 +29,7 @@ Here is a list of the problems available in the repository. Problems are organiz
 * [Merge Channels](09-merge-channels/)
 * [Concurrent Queue](10-concurrent-queue/)
 * [Concurrent Queue II](11-concurrent-queue-ii/)
+* [Concurrent Queue III](12-concurrent-queue-iii/)
 
 ## Contributing