TheAlgorithms/Java · error · IllegalArgumentException

baseNumbers must be non-empty.

Error message

baseNumbers must be non-empty.

What it means

Thrown by the NthUglyNumber constructor when baseNumbers is an empty int[]. Ugly numbers are defined relative to a set of prime bases; an empty base set makes the sequence undefined (there would be no candidates to generate). The constructor guards against this before initializing the positions list.

Source

Thrown at src/main/java/com/thealgorithms/maths/NthUglyNumber.java:30

 *   where the exponents a, b, c are non-negative integers.
 *   Some properties of ugly numbers:
 *     - base [2, 3, 5] ugly numbers are the 5-smooth numbers, cf. https://oeis.org/A051037
 *     - base [2, 3, 5, 7] ugly numbers are 7-smooth numbers, cf. https://oeis.org/A002473
 *     - base [2] ugly numbers are the non-negative powers of 2,
 *     - the base [2, 3, 5] ugly numbers are the same as base [5, 6, 2, 3, 5] ugly numbers
 */
public class NthUglyNumber {
    private ArrayList<Long> uglyNumbers = new ArrayList<>(singletonList(1L));
    private ArrayList<MutablePair<Integer, Integer>> positions = new ArrayList<>();

    /**
     * @brief initialized the object allowing to compute ugly numbers with given base
     * @param baseNumbers the given base of ugly numbers
     * @exception IllegalArgumentException baseNumber is empty
     */
    NthUglyNumber(final int[] baseNumbers) {
        if (baseNumbers.length == 0) {
            throw new IllegalArgumentException("baseNumbers must be non-empty.");
        }

        for (final var baseNumber : baseNumbers) {
            this.positions.add(MutablePair.of(baseNumber, 0));
        }
    }

    /**
     * @param n the zero-based-index of the queried ugly number
     * @exception IllegalArgumentException n is negative
     * @return the n-th ugly number (starting from index 0)
     */
    public Long get(final int n) {
        if (n < 0) {
            throw new IllegalArgumentException("n must be non-negative.");
        }

        while (uglyNumbers.size() <= n) {

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Supply at least one base number, e.g. {2, 3, 5} for the classic ugly-number definition.
2. Validate baseNumbers.length > 0 at the source (config loader, parser) before constructing the object.
3. If the base set is dynamic, short-circuit with a sensible default when the input collection is empty.

Example fix

// before
int[] base = new int[0];
NthUglyNumber u = new NthUglyNumber(base);

// after
int[] base = baseInput.length > 0 ? baseInput : new int[]{2, 3, 5};
NthUglyNumber u = new NthUglyNumber(base);

if (baseNumbers == null || baseNumbers.length == 0) {
    throw new IllegalArgumentException("baseNumbers must be non-empty");
}
NthUglyNumber u = new NthUglyNumber(baseNumbers);

When it happens

Trigger: Constructing new NthUglyNumber(new int[0]) or new NthUglyNumber(new int[]{}) — passing an empty array of base numbers.

Common situations: baseNumbers is loaded from configuration, a database column, or user input that was empty; a filter/map chain upstream reduced the array to zero elements; default-initializing the field to an empty array as a placeholder.

Related errors

• n must be non-negative.
• Input must be non-negative. Received:
• Input must be non-negative!
• Input must be non-negative!
• Input arrays cannot be empty.

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/5afdcaee0afd856f. Report an issue: GitHub.