小跟堆-会议室II

253. 会议室 II

给你一个会议时间安排的数组 intervals ，每个会议时间都会包括开始和结束的时间 intervals[i] = [starti, endi] ，返回 所需会议室的最小数量 。

示例 1：

输入： intervals = [[0,30],[5,10],[15,20]]
输出： 2

示例 2：

输入： intervals = [[7,10],[2,4]]
输出： 1

提示：

• 1 <= intervals.length <= 104
• 0 <= starti < endi <= 106

var minMeetingRooms = function(intervals) {
	intervals.sort((a, b) => a[0] - b[0]);
	const heap = new Heap((a, b) => a < b);
	let result = 0;
	for (let i = 0; i < intervals.length; i++) {
		const [start, end] = intervals[i];
		if ((!result && !heap.getSize()) || (heap.getSize() && start < heap.getTop())) {
			result++;
		}

		if (heap.getSize() && heap.getTop() <= start) {
			heap.pop();
		}

		heap.push(end);
	}

	return result;
}


class Heap {
	constructor(compare) {
		this.nodeList = [];
		this.compare = typeof compare === 'function' ? compare : this.defaultCompare;
	}

	defaultCompare(a, b) {
		return a > b;
	}

	getSize() {
		return this.nodeList.length;
	}

	getTop() {
		return this.nodeList[0];
	}

	push(value) {
		this.nodeList.push(value);
		this.up(this.nodeList.length - 1);
	}

	// 父结点的index值
	parent(index) {
		return index % 2 === 0 ? index / 2 - 1 : (index - 1) / 2;
	}

	up(index) {
		const { nodeList, compare, parent } = this;
		while (index > 0 && compare(nodeList[index], nodeList[parent(index)])) {
			const temp = nodeList[index];
			nodeList[index] = nodeList[parent(index)];
			nodeList[parent(index)] = temp;
			index = parent(index);
		}
	}

	pop() {
		if (this.nodeList.length === 0) {
			return null;
		}
		const top = this.nodeList[0];
		this.nodeList[0] = this.nodeList[this.nodeList.length - 1];
		this.nodeList.pop();
		if (this.nodeList.length > 1) {
			this.down(0);
		}
		return top;
	}

	left(index) {
		return index * 2 + 1;
	}

	right(index) {
		return index * 2 + 2;
	}

	down(index) {
		const { nodeList, left, right, compare } = this;
		while (left(index) < nodeList.length) {
			let target = left(index);
			if (right(index) < nodeList.length && compare(nodeList[right(index)], nodeList[left(index)])) {
				target = right(index);
			}
			if (compare(nodeList[index], nodeList[target])) {
				return;
			}
			const temp = nodeList[index];
			nodeList[index] = nodeList[target];
			nodeList[target] = temp;
			index = target;
		}
	}
}