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149 lines
3.9 KiB
Go
149 lines
3.9 KiB
Go
// Copyright (c) 2021, Emir Pasic. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package circularbuffer implements the circular buffer.
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//
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// In computer science, a circular buffer, circular queue, cyclic buffer or ring buffer is a data structure that uses a single, fixed-size buffer as if it were connected end-to-end. This structure lends itself easily to buffering data streams.
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//
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// Structure is not thread safe.
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//
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// Reference: https://en.wikipedia.org/wiki/Circular_buffer
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package circularbuffer
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import (
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"fmt"
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"strings"
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"github.com/emirpasic/gods/v2/queues"
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)
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// Assert Queue implementation
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var _ queues.Queue[int] = (*Queue[int])(nil)
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// Queue holds values in a slice.
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type Queue[T comparable] struct {
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values []T
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start int
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end int
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full bool
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maxSize int
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size int
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}
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// New instantiates a new empty queue with the specified size of maximum number of elements that it can hold.
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// This max size of the buffer cannot be changed.
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func New[T comparable](maxSize int) *Queue[T] {
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if maxSize < 1 {
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panic("Invalid maxSize, should be at least 1")
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}
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queue := &Queue[T]{maxSize: maxSize}
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queue.Clear()
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return queue
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}
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// Enqueue adds a value to the end of the queue
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func (queue *Queue[T]) Enqueue(value T) {
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if queue.Full() {
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queue.Dequeue()
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}
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queue.values[queue.end] = value
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queue.end = queue.end + 1
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if queue.end >= queue.maxSize {
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queue.end = 0
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}
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if queue.end == queue.start {
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queue.full = true
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}
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queue.size = queue.calculateSize()
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}
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// Dequeue removes first element of the queue and returns it, or the 0-value if queue is empty.
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// Second return parameter is true, unless the queue was empty and there was nothing to dequeue.
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func (queue *Queue[T]) Dequeue() (value T, ok bool) {
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if queue.Empty() {
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return value, false
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}
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value, ok = queue.values[queue.start], true
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queue.start = queue.start + 1
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if queue.start >= queue.maxSize {
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queue.start = 0
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}
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queue.full = false
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queue.size = queue.size - 1
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return
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}
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// Peek returns first element of the queue without removing it, or nil if queue is empty.
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// Second return parameter is true, unless the queue was empty and there was nothing to peek.
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func (queue *Queue[T]) Peek() (value T, ok bool) {
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if queue.Empty() {
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return value, false
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}
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return queue.values[queue.start], true
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}
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// Empty returns true if queue does not contain any elements.
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func (queue *Queue[T]) Empty() bool {
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return queue.Size() == 0
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}
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// Full returns true if the queue is full, i.e. has reached the maximum number of elements that it can hold.
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func (queue *Queue[T]) Full() bool {
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return queue.Size() == queue.maxSize
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}
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// Size returns number of elements within the queue.
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func (queue *Queue[T]) Size() int {
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return queue.size
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}
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// Clear removes all elements from the queue.
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func (queue *Queue[T]) Clear() {
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queue.values = make([]T, queue.maxSize, queue.maxSize)
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queue.start = 0
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queue.end = 0
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queue.full = false
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queue.size = 0
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}
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// Values returns all elements in the queue (FIFO order).
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func (queue *Queue[T]) Values() []T {
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values := make([]T, queue.Size(), queue.Size())
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for i := 0; i < queue.Size(); i++ {
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values[i] = queue.values[(queue.start+i)%queue.maxSize]
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}
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return values
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}
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// String returns a string representation of container
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func (queue *Queue[T]) String() string {
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str := "CircularBuffer\n"
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var values []string
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for _, value := range queue.Values() {
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values = append(values, fmt.Sprintf("%v", value))
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}
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str += strings.Join(values, ", ")
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return str
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}
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// Check that the index is within bounds of the list
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func (queue *Queue[T]) withinRange(index int) bool {
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return index >= 0 && index < queue.size
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}
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func (queue *Queue[T]) calculateSize() int {
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if queue.end < queue.start {
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return queue.maxSize - queue.start + queue.end
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} else if queue.end == queue.start {
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if queue.full {
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return queue.maxSize
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}
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return 0
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}
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return queue.end - queue.start
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}
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