Min-Heap Pop (Sift Down) - TypeScript DSA

Remove the minimum value, move the last item to the root, and sift downward.

Algorithm

Steps

Store the heap in an array.
Compare parent and child indexes instead of building explicit tree nodes.
Swap only when the heap order is violated.
Print the deterministic final heap state for replay comparison.

Complexity

Time: O(log n)
Space: O(1) extra

sift down After removing the root, the last value moves to the root and swaps with the smaller child until order is restored.

Visual walkthrough

TypeScript DSA Implementation

basic.ts

function listString(values: number[]): string { return `[${values.join(", ")}]`; }
function heapInsert(heap: number[], value: number): void {
  heap.push(value);
  let child = heap.length - 1;
  while (child > 0) {
    const parent = Math.floor((child - 1) / 2);
    if (heap[parent] <= heap[child]) break;
    [heap[parent], heap[child]] = [heap[child], heap[parent]];
    child = parent;
  }
}
function heapPop(heap: number[]): number {
  const smallest = heap[0];
  heap[0] = heap.pop()!;
  let parent = 0;
  while (true) {
    const left = parent * 2 + 1;
    const right = left + 1;
    if (left >= heap.length) break;
    let child = left;
    if (right < heap.length && heap[right] < heap[left]) child = right;
    if (heap[parent] <= heap[child]) break;
    [heap[parent], heap[child]] = [heap[child], heap[parent]];
    parent = child;
  }
  return smallest;
}
const heap: number[] = [1, 4, 2, 9, 6, 7];
const popped = heapPop(heap);
console.log(`${popped} -> ${listString(heap)}`);

After popping the minimum, the last value moves to the root and sifts down by swapping with the smaller child.

Step 1 - Replace root

The saved minimum is 1; the last value 7 moves to the root before sifting down.

Step 2 - Swap with the smaller child

7 swaps with 2, producing the final heap [2, 4, 7, 9, 6].

Output

1 -> [2, 4, 7, 9, 6]

Implementation notes

In TypeScript, heapPop(heap: number[]): number mutates the caller's number[]; the sample heap is explicitly declared as const heap: number[] = [1, 4, 2, 9, 6, 7].
const smallest = heap[0] stores the returned value, then heap[0] = heap.pop()! removes the last element and writes it to the root. The non-null assertion matches the checked non-empty sample heap.
The sift-down loop computes children with left = parent * 2 + 1 and right = left + 1, chooses the smaller numeric child when the right child is in bounds, and stops when heap[parent] <= heap[child].
Swaps use destructuring assignment on two heap slots, then advance parent to the child index. The trace shows [1, 4, 2, 9, 6, 7], root replacement to [7, 4, 2, 9, 6], then one swap with child 2 to [2, 4, 7, 9, 6].
The final console.log formats the popped value and heap as 1 -> [2, 4, 7, 9, 6]. Visible allocation is the initial heap array and output string; mutation is pop, root assignment, and one in-place swap.