/**
 * Dictionary encoding — store each distinct value once, then reference it.
 *
 * A column of city names repeats "Moscow" ten thousand times; PLAIN writes the
 * bytes ten thousand times, a dictionary writes them once and spends two BITS
 * per row pointing at them. This is the largest size win available to us short
 * of compression, and it costs no dependency.
 *
 * Whether to use it has to be decided from the DATA, and the decision must be
 * reproducible: a heuristic that consulted anything else — a clock, a memory
 * figure, a sampling rate — would put different bytes in the file on different
 * runs and break the cross-language contract the whole writer is built around.
 * So the rule below reads only the values.
 * Spec: docs/specs/2026-07-19-parquet-statistics-and-encodings.md §3
 */
import type { ColumnType } from '../column-type.js';
import type { TypedValue } from './convert.js';
export interface Dictionary {
    /** The distinct values, in first-seen order — the dictionary page's contents. */
    readonly values: TypedValue[];
    /** One index per present value, pointing into `values`. */
    readonly indices: number[];
}
/**
 * Build a dictionary for these values, or undefined when it would not pay.
 *
 * Returning undefined is the signal to keep PLAIN encoding — the caller must
 * not treat it as an error.
 */
export declare function buildDictionary(type: ColumnType, present: readonly TypedValue[]): Dictionary | undefined;
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