TheAlgorithms/Java · error · IllegalArgumentException

BeadSort cannot sort negative numbers.

Error message

BeadSort cannot sort negative numbers.

What it means

Thrown by BeadSort.sort(int[]) when any element is negative. BeadSort models each number as a count of beads on an abacus, which only works for non-negative integers; negative counts have no physical analog in the algorithm. The allInputsMustBeNonNegative helper scans the array before building the grid.

Solutions

1. Filter out or reject negative values before calling sort().
2. If negatives must be sorted, choose a comparison-based sort (e.g. Arrays.sort).
3. Offset all values by a constant to make them non-negative if the range is known and bounded.

Example fix

// before
int[] sorted = new BeadSort().sort(data);

// after
if (Arrays.stream(data).anyMatch(v -> v < 0)) throw new IllegalArgumentException("negatives not supported");
int[] sorted = new BeadSort().sort(data);

if (Arrays.stream(array).anyMatch(v -> v < 0)) throw new IllegalArgumentException("negatives not supported by BeadSort");

public static boolean isAllNonNegative(int[] a) { return IntStream.of(a).allMatch(v -> v >= 0); }

When it happens

Trigger: Calling sort(new int[]{3, -1, 2}); passing data containing negative deltas or signed measurements; merging arrays where one had negatives.

Common situations: Financial data with negative balances; temperature/sensor readings below zero; using BeadSort generically without checking the data domain.

Related errors

• Array contains negative integers.
• Array contains non-positive integers.
• Implementation cannot sort negative numbers.
• Input array must not be null.
• The input array cannot be null

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/77d5f39021f552b6. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/com/thealgorithms/sorts/BeadSort.java:22

public class BeadSort {
    private enum BeadState { BEAD, EMPTY }

    /**
     * Sorts the given array using the BeadSort algorithm.
     *
     * @param array The array of non-negative integers to be sorted.
     * @return The sorted array.
     * @throws IllegalArgumentException If the array contains negative numbers.
     */
    public int[] sort(int[] array) {
        allInputsMustBeNonNegative(array);
        return extractSortedFromGrid(fillGrid(array));
    }

    private void allInputsMustBeNonNegative(final int[] array) {
        if (Arrays.stream(array).anyMatch(s -> s < 0)) {
            throw new IllegalArgumentException("BeadSort cannot sort negative numbers.");
        }
    }

    private BeadState[][] fillGrid(final int[] array) {
        final var maxValue = Arrays.stream(array).max().orElse(0);
        var grid = getEmptyGrid(array.length, maxValue);

        int[] count = new int[maxValue];
        for (int i = 0, arrayLength = array.length; i < arrayLength; i++) {
            int k = 0;
            for (int j = 0; j < array[i]; j++) {
                grid[count[maxValue - k - 1]++][k] = BeadState.BEAD;
                k++;
            }
        }
        return grid;
    }

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