/**
 * In-place Fisher–Yates shuffle of `arr`.
 * Uses `Math.random()`; tests should stub `Math.random` for determinism.
 * @param arr Array to shuffle (mutated)
 * @returns The shuffled array (same reference)
 */
export declare function shuffle<T>(arr: T[]): T[];
/**
 * Draw `k` unique samples without replacement from `arr`.
 * If `k` >= arr.length a shallow copy is returned. Uses `Math.random()`.
 * @param arr Source array
 * @param k Number of samples to draw
 * @returns Array of sampled elements
 */
export declare function sample<T>(arr: T[], k: number): T[];
/**
 * Draw `k` bootstrap samples (with replacement) from `arr`.
 * Uses `Math.random()`; tests should stub `Math.random` for determinism.
 * @param arr Source array
 * @param k Number of draws
 * @returns Array of sampled elements (with replacement)
 */
export declare function bootstrap<T>(arr: T[], k: number): T[];