TheAlgorithms/Java · error · IllegalArgumentException

Probability should be from 0 to 1. But was: ${probability}

Error message

Probability should be from 0 to 1. But was: ${probability}

What it means

Thrown by SkipList.BernoulliHeightStrategy(double probability) when probability is <= 0 or >= 1. The strategy uses probability to compute the geometric height formula `log(expectedSize)/log(1/probability)`, which divides by zero or is undefined at the boundaries. The library requires an open interval (0, 1).

Source

Thrown at src/main/java/com/thealgorithms/datastructures/lists/SkipList.java:303

     * <p>
     * Maximum height that would give the best search complexity
     * calculated by <code>log<sub>1/p</sub>n</code>
     * where {@code n} is an expected count of elements in list.
     */
    public static class BernoulliHeightStrategy implements HeightStrategy {

        private final double probability;

        private static final double DEFAULT_PROBABILITY = 0.5;
        private static final Random RANDOM = new Random();

        public BernoulliHeightStrategy() {
            this.probability = DEFAULT_PROBABILITY;
        }

        public BernoulliHeightStrategy(double probability) {
            if (probability <= 0 || probability >= 1) {
                throw new IllegalArgumentException("Probability should be from 0 to 1. But was: " + probability);
            }
            this.probability = probability;
        }

        @Override
        public int height(int expectedSize) {
            long height = Math.round(Math.log10(expectedSize) / Math.log10(1 / probability));
            if (height > Integer.MAX_VALUE) {
                throw new IllegalArgumentException();
            }
            return (int) height;
        }

        @Override
        public int nodeHeight(int heightCap) {
            int level = 0;
            double border = 100 * (1 - probability);
            while (((RANDOM.nextInt(Integer.MAX_VALUE) % 100) + 1) > border) {

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Use the no-arg constructor BernoulliHeightStrategy() for the default 0.5.
2. Validate probability is strictly between 0 and 1 before constructing.
3. Clamp external config values into (0, 1) with a small epsilon.
4. Audit any ratio that feeds probability to ensure it cannot reach 0 or 1.

Example fix

// before
new BernoulliHeightStrategy(prob); // prob may be 0 or 1

// after
if (prob <= 0 || prob >= 1) {
    prob = 0.5; // sane default
}
new BernoulliHeightStrategy(prob);

if (probability > 0 && probability < 1) {
    new BernoulliHeightStrategy(probability);
} else {
    new BernoulliHeightStrategy(); // default 0.5
}

try {
    new BernoulliHeightStrategy(probability);
} catch (IllegalArgumentException e) {
    new BernoulliHeightStrategy();
}

When it happens

Trigger: Constructing BernoulliHeightStrategy with 0.0 or 1.0. Loading probability from a config file where the value was set to a boundary. Computing probability from a ratio that can hit exactly 0 or 1.

Common situations: Config typos setting probability to 1 or 0. Probability derived from count/total where count == 0 or count == total. Defaulting to the constructor's 0.5 is safe, but explicit boundary values are rejected.

Related errors

• Size must be greater than 0
• Cannot extract from empty heap
• Cannot insert null element
• Cannot delete from empty heap
• MinPriorityQueue is full. Cannot insert new element.

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/18bc4c24432951ca. Report an issue: GitHub.