TheAlgorithms/C-Sharp · error · ArgumentException

The parameter's value is invalid.

Error message

The parameter's value is invalid.

What it means

RebuildFromList rebuilds a balanced subtree of scapegoat-tree nodes from a list slice delimited by [start, end]. It throws ArgumentException when start is greater than end, meaning the requested window is inverted and cannot define a subtree. The parameter named in the exception is `start`.

Solutions

1. Ensure start <= end before calling RebuildFromList; swap or normalize the indexes if needed.
2. Decide explicitly how an empty range should behave (return null or skip the rebuild) and guard before calling.
3. Validate computed indexes against the list bounds as well (0 <= start, end < list.Count).

Example fix

// before
var node = Node<TKey>.RebuildFromList(nodes, end, start);
// after
if (start > end) (start, end) = (end, start);
var node = Node<TKey>.RebuildFromList(nodes, start, end);

if (list is null || start < 0 || end >= list.Count || start > end) throw new ArgumentOutOfRangeException(nameof(start), "Require 0 <= start <= end < list.Count");

static bool IsValidRange<T>(int start, int end) => start <= end;

When it happens

Trigger: Calling RebuildFromList with start > end, e.g. passing indexes in the wrong order or computing an empty/negative-length range.

Common situations: Off-by-one errors when slicing node lists after collecting an in-order path; passing (end, start) swapped; callers that computed an empty range (start == end+1) instead of handling it separately.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Graph capacity should always be a non-negative integer.
• The path collection should not be empty.
• The alpha parameter's value should be in 0.5..1.0 range.
• Invalid parameter settings for Ascon Hash
• Cash flows list cannot be empty

AI-assisted analysis of TheAlgorithms/C-Sharp@96e2905cab (2026-09-13). Data as JSON: /api/errors/9a646d15d47ad0c6. Report an issue: GitHub.

Appendix: source

Thrown at DataStructures/ScapegoatTree/Extensions.cs:41

        }
    }

    /// <summary>
    /// Rebuilds a scapegoat tree from list of nodes.
    /// Use with <see cref="FlattenTree{TKey}"/> method.
    /// </summary>
    /// <param name="list">Flattened tree.</param>
    /// <param name="start">Start index.</param>
    /// <param name="end">End index.</param>
    /// <typeparam name="TKey">Scapegoat tree node key type.</typeparam>
    /// <returns>Scapegoat tree root node.</returns>
    /// <exception cref="ArgumentException">Thrown if start index is invalid.</exception>
    public static Node<TKey> RebuildFromList<TKey>(IList<Node<TKey>> list, int start, int end)
        where TKey : IComparable
    {
        if (start > end)
        {
            throw new ArgumentException("The parameter's value is invalid.", nameof(start));
        }

        var pivot = Convert.ToInt32(Math.Ceiling(start + (end - start) / 2.0));

        return new Node<TKey>(list[pivot].Key)
        {
            Left = start > (pivot - 1) ? null : RebuildFromList(list, start, pivot - 1),
            Right = (pivot + 1) > end ? null : RebuildFromList(list, pivot + 1, end),
        };
    }
}

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