Smallest Range Covering Elements from K Lists.js

var smallestRange = function(nums) {
    let minHeap = new MinPriorityQueue({
        compare: (a,b) => a[0] - b[0]
    });
    let start = 0, end = Infinity;
    let maxSoFar = -Infinity;
	
    for (let num of nums) {
        minHeap.enqueue([num[0], 0, num]);
        maxSoFar = Math.max(maxSoFar, num[0]);
    }
	
    while (minHeap.size() == nums.length) {
        let [num, i, list] = minHeap.dequeue();
        
        if (end - start > maxSoFar - num) {
            start = num;
            end = maxSoFar;
        }
        
        if (list.length > i + 1) {
            minHeap.enqueue([list[i + 1], i + 1, list]);
            maxSoFar = Math.max(maxSoFar, list[i + 1]);
        }
    }
    
    return [start, end];
};