/** @import { Metric } from "../metrics/index.js" */
/** @import { ParametersBallTree } from "./index.js" */
/**
 * @template {number[] | Float64Array} T
 * @typedef {Object} ElementWithIndex
 * @property {number} index
 * @property {T} element
 */
/**
 * Ball Tree for efficient nearest neighbor search.
 *
 * A Ball Tree is a metric tree that partitions points into a nested set of
 * hyperspheres (balls). It is particularly effective for high-dimensional
 * data and supports any valid metric.
 *
 * @class
 * @category KNN
 * @template {number[] | Float64Array} T
 * @extends KNN<T, ParametersBallTree>
 */
export class BallTree<T extends number[] | Float64Array> extends KNN<T, ParametersBallTree> {
  /**
   * Generates a BallTree with given `elements`.
   *
   * @param {T[]} elements - Elements which should be added to the BallTree
   * @param {ParametersBallTree} [parameters={metric: euclidean}] Default is `{metric: euclidean}`
   * @see {@link https://en.wikipedia.org/wiki/Ball_tree}
   * @see {@link https://github.com/invisal/noobjs/blob/master/src/tree/BallTree.js}
   */
  constructor(elements: T[], parameters?: ParametersBallTree);
  /**
   * @private
   * @type {BallTreeNode<T> | BallTreeLeaf<T>}
   */
  private _root;
  /** @returns {Metric} */
  get _metric(): Metric;
  /**
   * @private
   * @param {ElementWithIndex<T>[]} elements
   * @returns {BallTreeNode<T> | BallTreeLeaf<T>} Root of balltree.
   */
  private _construct;
  /**
   * @private
   * @param {ElementWithIndex<T>[]} B
   * @returns {number}
   */
  private _greatest_spread;
  /**
   * @param {number} i
   * @param {number} k
   */
  search_by_index(
    i: number,
    k?: number,
  ): {
    element: T;
    index: number;
    distance: number;
  }[];
  /**
   * @param {T} t - Query element.
   * @param {number} [k=5] - Number of nearest neighbors to return. Default is `5`
   * @returns {{ element: T; index: number; distance: number }[]} - List consists of the `k` nearest neighbors.
   */
  search(
    t: T,
    k?: number,
  ): {
    element: T;
    index: number;
    distance: number;
  }[];
  /**
   * @private
   * @param {T} t - Query element.
   * @param {number} k - Number of nearest neighbors to return.
   * @param {Heap<ElementWithIndex<T>>} Q - Heap consists of the currently found `k` nearest neighbors.
   * @param {BallTreeNode<T> | BallTreeLeaf<T>} B
   */
  private _search;
}
export type ElementWithIndex<T extends number[] | Float64Array> = {
  index: number;
  element: T;
};
import type { ParametersBallTree } from "./index.js";
import { KNN } from "./KNN.js";
import type { Metric } from "../metrics/index.js";
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