Given m number of sorted lists in ascending order and an integer k, find the kth smallest number among all the given lists.

1-smallest-in-sorted-lists.js

export function kSmallestNumber(lists, k) {
  const heap = new MinHeap();

  // initialize by pushing first element of each list into heap
  for (let i = 0; i < lists.length; ++i) {
    const list = lists[i];
    if (list[0] != null) {
      heap.offer([list[0], i, 0]);
    }
  }

  // this is our last popped element
  // since we pop elements from the heap in sorted order,
  // after k pops, it will be our kth smallest element
  let pop = 0;
  // keep track of pops from heap, we need to do k pops to find kth smallest element
  let count = 0;
  while (count < k && heap.size() > 0) {
    const [value, listIndex, elementIndex] = heap.poll();
    pop = value;
    count += 1;
    // after pop, add the next element from the same list into the heap
    const nextIndex = elementIndex + 1;
    const nextValue = lists[listIndex][nextIndex];
    if (nextValue != null) {
      heap.offer([nextValue, listIndex, nextIndex]);
    }
  }

  return pop;
}

2-README.md

Where m is how many lists we have.