/** FIFO with amortized O(1) removal, without Array.shift on each item. */
export function createDeque<T>() {
  let items: T[] = [], head = 0;
  return {
    get size() { return items.length - head; },
    push(value: T) { items.push(value); },
    peek(): T | undefined { return items[head]; },
    pop(): T | undefined {
      if (head === items.length) return undefined;
      const value = items[head++];
      if (head > 1024 && head * 2 >= items.length) { items = items.slice(head); head = 0; }
      return value;
    },
    clear() { items = []; head = 0; },
    values() { return items.slice(head); },
  };
}
export function createMinHeap<T>(compare: (left: T, right: T) => number) {
  const items: T[] = [];
  return {
    get size() { return items.length; },
    peek(): T | undefined { return items[0]; },
    push(value: T) {
      let index = items.length; items.push(value);
      while (index > 0) { const parent = (index - 1) >> 1; if (compare(items[parent], value) <= 0) break; items[index] = items[parent]; index = parent; }
      items[index] = value;
    },
    pop(): T | undefined {
      if (!items.length) return undefined;
      const first = items[0], last = items.pop()!;
      if (items.length) {
        let index = 0;
        while (index * 2 + 1 < items.length) {
          let child = index * 2 + 1;
          if (child + 1 < items.length && compare(items[child + 1], items[child]) < 0) child++;
          if (compare(last, items[child]) <= 0) break;
          items[index] = items[child]; index = child;
        }
        items[index] = last;
      }
      return first;
    },
    clear() { items.length = 0; },
  };
}