/**
* Definition for singly-linked list.
* function ListNode(val, next) {
* this.val = (val===undefined ? 0 : val)
* this.next = (next===undefined ? null : next)
* }
*/
/**
* @param {ListNode[]} lists
* @return {ListNode}
*/
var mergeKLists = function (lists) {
if (!lists || !lists.length) return null;
let dummy = new ListNode();
let tail = dummy;
const heap = new MinHeap(lists.filter(Boolean), function comparator(inserted, compared) {
return inserted.val > compared.val;
});
while (heap.size() > 0) {
const min = heap.pop();
tail.next = new ListNode(min.val);
tail = tail.next;
min.next && heap.insert(min.next)
}
return dummy.next;
};
// **************************************************
class Heap {
constructor(list = [], comparator) {
this.list = list;
this.comparator = comparator;
this.init();
}
init() {
const size = this.size();
for (let i = Math.floor(size / 2) - 1; i >= 0; i--) {
this.heapify(this.list, size, i);
}
}
insert(n) {
this.list.push(n);
const size = this.size();
for (let i = Math.floor(size / 2) - 1; i >= 0; i--) {
this.heapify(this.list, size, i);
}
}
peek() {
return this.list[0];
}
pop() {
const last = this.list.pop();
if (this.size() === 0) return last;
const returnItem = this.list[0];
this.list[0] = last;
this.heapify(this.list, this.size(), 0);
return returnItem;
}
size() {
return this.list.length;
}
}
class MinHeap extends Heap {
constructor(list, comparator) {
if (typeof comparator != 'function') {
comparator = function comparator(inserted, compared) {
return inserted > compared;
};
}
super(list, comparator);
}
heapify(arr, size, i) {
let smallest = i;
const left = Math.floor(i * 2 + 1);
const right = Math.floor(i * 2 + 2);
if (left < size && this.comparator(arr[smallest], arr[left]))
smallest = left;
if (right < size && this.comparator(arr[smallest], arr[right]))
smallest = right;
if (smallest !== i) {
[arr[smallest], arr[i]] = [arr[i], arr[smallest]];
this.heapify(arr, size, smallest);
}
}
}