src/priority-queue.ts

   1 // Copyright Jerome Benoit. 2024. All Rights Reserved.
   2
   3 /**
   4  * Priority queue node.
   5  *
   6  * @typeParam T - Type of priority queue node data.
   7  * @internal
   8  */
   9 export interface PriorityQueueNode<T> {
  10   data: T
  11   priority: number
  12 }
  13
  14 /**
  15  * Priority queue.
  16  *
  17  * @typeParam T - Type of priority queue data.
  18  * @internal
  19  */
  20 export class PriorityQueue<T> {
  21   private nodeArray!: Array<PriorityQueueNode<T>>
  22   /** Prioritized bucket size. */
  23   private readonly k: number
  24   /** The size of the priority queue. */
  25   public size!: number
  26   /** The maximum size of the priority queue. */
  27   public maxSize!: number
  28
  29   /**
  30    * The number of filled prioritized buckets.
  31    */
  32   public get buckets (): number {
  33     return this.k === Infinity ? 1 : Math.trunc(this.nodeArray.length / this.k)
  34   }
  35
  36   /**
  37    * Constructs a priority queue.
  38    *
  39    * @param k - Prioritized bucket size. @defaultValue Infinity
  40    */
  41   public constructor (k = Infinity) {
  42     if (k !== Infinity && !Number.isSafeInteger(k)) {
  43       throw new TypeError('k must be an integer')
  44     }
  45     if (k < 1) {
  46       throw new RangeError('k must be greater than or equal to 1')
  47     }
  48     this.k = k
  49     this.clear()
  50   }
  51
  52   /**
  53    * Enqueue data into the priority queue.
  54    *
  55    * @param data - Data to enqueue.
  56    * @param priority - Priority of the data. Lower values have higher priority.
  57    * @returns The new size of the priority queue.
  58    */
  59   public enqueue (data: T, priority?: number): number {
  60     priority = priority ?? 0
  61     const startIndex = this.k === Infinity ? 0 : this.buckets * this.k
  62     let inserted = false
  63     for (let index = startIndex; index < this.nodeArray.length; index++) {
  64       if (this.nodeArray[index].priority > priority) {
  65         this.nodeArray.splice(index, 0, { data, priority })
  66         inserted = true
  67         break
  68       }
  69     }
  70     if (!inserted) {
  71       this.nodeArray.push({ data, priority })
  72     }
  73     return this.incrementSize()
  74   }
  75
  76   /**
  77    * Dequeue data from the priority queue.
  78    *
  79    * @param bucket - The prioritized bucket to dequeue from. @defaultValue 0
  80    * @returns The dequeued data or `undefined` if the priority queue is empty.
  81    */
  82   public dequeue (bucket = 0): T | undefined {
  83     if (this.k !== Infinity && bucket > 0) {
  84       while (bucket > 0) {
  85         const index = bucket * this.k
  86         // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
  87         if (this.nodeArray[index] != null) {
  88           --this.size
  89           return this.nodeArray.splice(index, 1)[0].data
  90         }
  91         --bucket
  92       }
  93     }
  94     if (this.size > 0) {
  95       --this.size
  96     }
  97     return this.nodeArray.shift()?.data
  98   }
  99
 100   /**
 101    * Peeks at the first data.
 102    * @returns The first data or `undefined` if the priority queue is empty.
 103    */
 104   public peekFirst (): T | undefined {
 105     return this.nodeArray[0]?.data
 106   }
 107
 108   /**
 109    * Peeks at the last data.
 110    * @returns The last data or `undefined` if the priority queue is empty.
 111    */
 112   public peekLast (): T | undefined {
 113     return this.nodeArray[this.nodeArray.length - 1]?.data
 114   }
 115
 116   /**
 117    * Clears the priority queue.
 118    */
 119   public clear (): void {
 120     this.nodeArray = []
 121     this.size = 0
 122     this.maxSize = 0
 123   }
 124
 125   /**
 126    * Returns an iterator for the priority queue.
 127    *
 128    * @returns An iterator for the priority queue.
 129    * @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols
 130    */
 131   [Symbol.iterator] (): Iterator<T> {
 132     let i = 0
 133     return {
 134       next: () => {
 135         if (i >= this.nodeArray.length) {
 136           return {
 137             value: undefined,
 138             done: true
 139           }
 140         }
 141         const value = this.nodeArray[i].data
 142         i++
 143         return {
 144           value,
 145           done: false
 146         }
 147       }
 148     }
 149   }
 150
 151   /**
 152    * Increments the size of the priority queue.
 153    *
 154    * @returns The new size of the priority queue.
 155    */
 156   private incrementSize (): number {
 157     ++this.size
 158     if (this.size > this.maxSize) {
 159       this.maxSize = this.size
 160     }
 161     return this.size
 162   }
 163 }