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195 lines (181 loc) · 4.78 KB
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/**
* A binary heap is a complete binary tree which
* satisfies the heap ordering property.
*
* @example
* var Heap = require('path-to-algorithms/src/data-structures/heap').Heap;
*
* var heap = new Heap(function(a, b) {
* return a.birthyear - b.birthyear;
* });
*
* heap.add({
* name: 'John',
* birthyear: 1981
* });
* heap.add({
* name: 'Pavlo',
* birthyear: 2000
* });
* heap.add({
* name: 'Garry',
* birthyear: 1989
* });
* heap.add({
* name: 'Derek',
* birthyear: 1990
* });
* heap.add({
* name: 'Ivan',
* birthyear: 1966
* });
*
* console.log(heap.extract()); // { name: 'Pavlo', birthyear: 2000 }
* console.log(heap.extract()); // { name: 'Derek', birthyear: 1990 }
* console.log(heap.extract()); // { name: 'Garry', birthyear: 1989 }
* console.log(heap.extract()); // { name: 'John', birthyear: 1981 }
* console.log(heap.extract()); // { name: 'Ivan', birthyear: 1966 }
*
* @module data-structures/heap
*/
(function (exports) {
'use strict';
/**
* Minimum heap constructor.
*
* @public
* @constructor
* @param {Function} cmp Function used for comparison between the elements.
*/
exports.Heap = function (cmp) {
this._heap = [];
if (typeof cmp === 'function') {
this._cmp = cmp;
} else {
this._cmp = function (a, b) {
return a - b;
};
}
};
/**
* Exchange indexes with start index given as argument
* to turn the tree into a valid heap. On a single call
* this method maintains only a single "branch" of the heap.<br><br>
*
* Time complexity: O(log N).
*
* @private
* @param {Number} index The parent.
*/
exports.Heap.prototype._heapify = function (index) {
var extr = index;
var left = 2 * index + 1;
var right = 2 * index + 2;
var temp;
if (left < this._heap.length &&
this._cmp(this._heap[left], this._heap[index]) > 0) {
extr = left;
}
if (right < this._heap.length &&
this._cmp(this._heap[right], this._heap[index]) > 0 &&
this._cmp(this._heap[right], this._heap[left]) > 0) {
extr = right;
}
if (index !== extr) {
temp = this._heap[index];
this._heap[index] = this._heap[extr];
this._heap[extr] = temp;
this._heapify(extr);
}
};
/**
* Changes the key.<br><br>
* Complexity: O(log N).
*
* @public
* @param {Number} index Index of the value which should be changed.
* @param {Number|Object} value New value according to the index.
* @return {Number} New position of the element.
*/
exports.Heap.prototype.changeKey = function (index, value) {
this._heap[index] = value;
var elem = this._heap[index];
var parent = Math.floor(index / 2);
var temp;
if (elem !== undefined) {
while (parent >= 0 && this._cmp(elem, this._heap[parent]) > 0) {
temp = this._heap[parent];
this._heap[parent] = elem;
this._heap[index] = temp;
index = parent;
parent = Math.floor(parent / 2);
}
this._heapify(index);
}
return parent;
};
/**
* Updates a given node. This operation is useful
* in algorithms like Dijkstra, A* where we need
* to decrease/increase value of the given node.
*
* @public
* @param {Number|Object} node Node which should be updated.
*/
exports.Heap.prototype.update = function (node) {
var idx = this._heap.indexOf(node);
if (idx >= 0) {
this.changeKey(idx, node);
}
};
/**
* Adds new element to the heap.<br><br>
* Complexity: O(log N).
*
* @public
* @param {Number|Object} value Value which will be inserted.
* @return {Number} Index of the inserted value.
*/
exports.Heap.prototype.add = function (value) {
this._heap.push(value);
return this.changeKey(this._heap.length - 1, value);
};
/**
* Returns current value which is on the top of the heap.<br><br>
* Complexity: O(1).
*
* @public
* @return {Number|Object} Current top value.
*/
exports.Heap.prototype.top = function () {
return this._heap[0];
};
/**
* Removes and returns the current extremum value
* which is on the top of the heap.<br><br>
* Complexity: O(log N).
*
* @public
* @returns {Number|Object} The extremum value.
*/
exports.Heap.prototype.extract = function () {
if (!this._heap.length) {
throw 'The heap is already empty!';
}
var extr = this._heap.shift();
this._heapify(0);
return extr;
};
exports.Heap.prototype.getCollection = function () {
return this._heap;
};
/**
* Checks or heap is empty.
*
* @public
* @returns {Boolean} Returns true if heap is empty.
*/
exports.Heap.prototype.isEmpty = function () {
return !this._heap.length;
};
})(typeof window === 'undefined' ? module.exports : window);