用NodeJs實現優先級隊列PQueue

優先級隊列（PriorityQueue）是個很有用的數據結構，很多編程語言都有實現。NodeJs是一個比較新潮的服務器語言，貌似還沒有提供相關類。這些天有用到優先級隊列，因為時間很充足，閑來無事，就自己實現了一下。代碼如下：

/**
 * script: pqueue.js
 * description: 優先級隊列類
 * authors: [e-mail]
 * date: 2016-04-19
 */

var util = require('util');

/**
 * 優先級隊列類
 * @param cmp_func 優先級比較函數，必需，參考數組排序參數
 */
var PQueue = exports.PQueue = function(cmp_func) {
    //記錄數組
    this._records = [];
    //優先級比較方法
    this._cmp_func = cmp_func;
};

//堆向上調整
PQueue.prototype._heapUpAdjust = function(index) {
    var records = this._records;
    var record = records[index];
    var cmp_func = this._cmp_func;
    while (index > 0) {
        var parent_index = Math.floor((index - 1) / 2);
        var parent_record = records[parent_index];
        if (cmp_func(record, parent_record) < 0) {
            records[index] = parent_record;
            index = parent_index;
        } else {
            break;
        }
    }
    records[index] = record;
};

//堆向下調整
PQueue.prototype._heapDownAdjust = function(index) {
    var records = this._records;
    var record = records[index];
    var cmp_func = this._cmp_func;
    var length = records.length;
    var child_index = 2 * index + 1;
    while (child_index < length) {
        if (child_index + 1 < length && cmp_func(records[child_index], records[child_index + 1]) > 0) {
            child_index ++;
        }
        var child_record = records[child_index];
        if (cmp_func(record, child_record) > 0) {
            records[index] = child_record;
            index = child_index;
            child_index = 2 * index + 1;
        } else {
            break;
        }
    }
    records[index] = record;
};

//銷毀
PQueue.prototype.destroy = function() {
    this._records = null;
    this._cmp_func = null;
};

//將記錄插入隊列
PQueue.prototype.enQueue = function(record) {
    var records = this._records;
    records.push(record);
    this._heapUpAdjust(records.length - 1);
};

//刪除並返回隊頭記錄
PQueue.prototype.deQueue = function() {
    var records = this._records;
    if (!records.length)
        return undefined;
    var record = records[0];
    if (records.length == 1) {
        records.length = 0;
    } else {
        records[0] = records.pop();
        this._heapDownAdjust(0);
    }
    return record;
};

//獲取隊頭記錄
PQueue.prototype.getHead = function() {
    return this._records[0];
};

//獲取隊列長度
PQueue.prototype.getLength = function() {
    return this._records.length;
};

//判斷隊列是否為空
PQueue.prototype.isEmpty = function() {
    return this._records.length == 0;
};

//清空隊列
PQueue.prototype.clear = function() {
    this._records.length = 0;
};

 我覺得，相對於其他排序算法而言，用堆實現優先級隊列，入隊時間波動較小，比較平穩。