js 判断数组第二大的数

在2022年二月份有很多前端的朋友面试大厂会问到了js 判断数组第二大的数的题（其实就是一道算法题，在力扣题号为：215，题目为：数组中的第K个最大元素

<script type="text/javascript">
//访问网址：https://xuexiluxian.cn/
var findKthLargest = function(nums, k) {
    let arr = new MinHeap();
    nums.forEach(item=>{
        arr.insert( item );
        if( arr.size() > k ){
            arr.pop();
        }
    })
    return arr.peek();
};
findKthLargest([3,2,1,5,6,4],2);

class MinHeap{
	constructor(){
		this.heap = [];
	}
	//换位置
	swap(i1,i2){
		const temp = this.heap[i1];
		this.heap[i1] = this.heap[i2];
		this.heap[i2] = temp;
	}
	//找到父节点
	getParentIndex( index ){
		return Math.floor( (index-1)/2  );
	}
	//上(前)移操作
	up( index ){
		//如果是0就不移动了
		if( index ==0 )return;
		const parentIndex = this.getParentIndex( index );
		//如果父元素大于当前元素,就开始移动
		if( this.heap[parentIndex] > this.heap[index] ){
			this.swap(  parentIndex  ,  index );
			this.up( parentIndex );
		}
	} 
	//获取左侧子节点
	getLeftIndex( index ){
		return index * 2 + 1;
	}
	//获取右侧子节点
	getRightIndex( index ){
		return index * 2 + 2;
	}
	//下(后)移操作
	down( index ){
		const leftIndex = this.getLeftIndex( index );
		const rightIndex = this.getRightIndex( index );
		if( this.heap[leftIndex] < this.heap[index] ){
			this.swap(leftIndex,index);
			this.down( leftIndex );
		}
		if( this.heap[rightIndex] < this.heap[index] ){
			this.swap(rightIndex,index);
			this.down( rightIndex );
		}
	}
	//添加元素
	insert( value ){
		this.heap.push( value );
		this.up( this.heap.length-1 );
	}
	//删除堆顶
	pop(){
		this.heap[0] = this.heap.pop();
		this.down( 0 );
	}
	//获取堆顶
	peek(){
		return this.heap[0]
	}
	size(){
		return this.heap.length;
	}

}
</script>