Code Review (Easy): The Unified Activity Stream

Story

Lena was working on a new dashboard for ReviewThat Labs that combines activity feeds from several different microservices. Each service provides its own list of events already sorted by time, but she needs to display them all together in a single, chronologically ordered master feed. Eva reviewed the initial prototype and suggested creating a reusable helper to merge any number of these streams into one. For instance, if the team receives three separate lists of timestamps like [1, 4, 5], [1, 3, 4], and [2, 6], the utility should output a single unified sequence of [1, 1, 2, 3, 4, 4, 5, 6].

Your Task

Read the story and code, then decide if the code is ready for production or needs improvement.

Hints

What would block an approval? Give me a hint.

Check out Next Topic: Unified Event Timelines

class ListNode {
  val: number;
  next: ListNode | null;
  constructor(val?: number, next?: ListNode | null) {
    this.val = val === undefined ? 0 : val;
    this.next = next === undefined ? null : next;
  }
}

class MinHeap {
  private heap: ListNode[] = [];

size(): number {
    return this.heap.length;
  }

push(node: ListNode) {
    this.heap.push(node);
    this.siftUp(this.heap.length - 1);
  }

pop(): ListNode | null {
    const n = this.heap.length;
    if (n === 0) return null;
    if (n === 1) return this.heap.pop() || null;
    const top = this.heap[0];
    this.heap[0] = this.heap.pop() as ListNode;
    this.siftDown(0);
    return top;
  }

private siftUp(idx: number) {
    while (idx > 0) {
      const parent = (idx - 1) >> 1;
      if (this.heap[idx].val < this.heap[parent].val) {
        this.swap(idx, parent);
        idx = parent;
      } else break;
    }
  }

private siftDown(idx: number) {
    const n = this.heap.length;
    while (true) {
      const left = (idx << 1) + 1;
      const right = left + 1;
      let smallest = idx;
      if (left < n && this.heap[left].val < this.heap[smallest].val) smallest = left;
      if (right < n && this.heap[right].val < this.heap[smallest].val) smallest = right;
      if (smallest === idx) break;
      this.swap(idx, smallest);
      idx = smallest;
    }
  }

private swap(i: number, j: number) {
    const tmp = this.heap[i];
    this.heap[i] = this.heap[j];
    this.heap[j] = tmp;
  }
}