export class MinHeap {
  constructor() { this.items = []; }
  push(item) {
    this.items.push(item);
    let i = this.items.length - 1;
    while (i > 0) {
      const parent = (i - 1) >> 1;
      if (this.items[parent].f <= item.f) break;
      this.items[i] = this.items[parent];
      i = parent;
    }
    this.items[i] = item;
  }
  pop() {
    if (this.items.length === 0) return null;
    const root = this.items[0];
    const last = this.items.pop();
    if (this.items.length > 0) {
      let i = 0;
      while (true) {
        const left = i * 2 + 1;
        const right = left + 1;
        if (left >= this.items.length) break;
        const child = right < this.items.length && this.items[right].f < this.items[left].f ? right : left;
        if (this.items[child].f >= last.f) break;
        this.items[i] = this.items[child];
        i = child;
      }
      this.items[i] = last;
    }
    return root;
  }
  get length() { return this.items.length; }
}