TheAlgorithms/C-Sharp · error · ArgumentException

The alpha parameter's value should be in 0.5..1.0 range.

Error message

The alpha parameter's value should be in 0.5..1.0 range.

What it means

CheckAlpha validates the alpha weight-balance parameter of ScapegoatTree. Alpha must lie in [0.5, 1.0]; values below 0.5 would demand impossible balance and above 1.0 disable rebalancing checks. Invalid values passed to the constructor or Tune throw ArgumentException naming `alpha`.

Solutions

1. Clamp or validate alpha to the 0.5..1.0 range before constructing/tuning.
2. If the value comes from config as a percentage, divide by 100 first.
3. Check for NaN/parse failures when alpha originates from user input.

Example fix

// before
var tree = new ScapegoatTree<int>(75);
// after
var alpha = 75 / 100.0;
var tree = new ScapegoatTree<int>(alpha);

if (double.IsNaN(alpha) || alpha < 0.5 || alpha > 1.0) throw new ArgumentOutOfRangeException(nameof(alpha), alpha, "alpha must be in [0.5, 1.0]");

static bool IsValidAlpha(double alpha) => !double.IsNaN(alpha) && alpha >= 0.5 && alpha <= 1.0;

try { tree.Tune(alpha); } catch (ArgumentException ex) { logger.LogWarning(ex, "Invalid alpha, keeping previous value"); }

When it happens

Trigger: new ScapegoatTree<double>(alpha) or tree.Tune(alpha) with alpha < 0.5 or alpha > 1.0, including NaN comparisons failing the range pattern.

Common situations: Config-driven alpha read from app settings as a percentage (e.g. 75 instead of 0.75), inverted bounds like 1.5, or a misparsed decimal separator.

Understand the failure class

Background: "value must be between 0 and 1" / "out of range" / "must not be negative" errors: fixing range-validation failures across open-source libraries — this error's family across 42 libraries.

Related errors

• The parameter's value is invalid.
• The path collection should not be empty.
• Invalid parameter settings for Ascon Hash
• Cash flows list cannot be empty
• cannot be negative

AI-assisted analysis of TheAlgorithms/C-Sharp@96e2905cab (2026-09-13). Data as JSON: /api/errors/09a56101ea16cf7a. Report an issue: GitHub.

Appendix: source

Thrown at DataStructures/ScapegoatTree/ScapegoatTree.cs:273

        while (path.TryPop(out var next))
        {
            if (depth > next.GetAlphaHeight(Alpha))
            {
                return path.TryPop(out var parent) ? (parent, next) : (null, next);
            }

            depth++;
        }

        throw new InvalidOperationException("Scapegoat node wasn't found. The tree should be unbalanced.");
    }

    private static void CheckAlpha(double alpha)
    {
        if (alpha is < 0.5 or > 1.0)
        {
            throw new ArgumentException("The alpha parameter's value should be in 0.5..1.0 range.", nameof(alpha));
        }
    }

    private bool Remove(Node<TKey>? parent, Node<TKey>? node, TKey key)
    {
        if (node is null || parent is null)
        {
            return false;
        }

        var compareResult = node.Key.CompareTo(key);

        if (compareResult > 0)
        {
            return Remove(node, node.Left, key);
        }

        if (compareResult < 0)

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