C#•3y ago

Levenshtein distance method throwing `IndexOutOfRangeException` [Answered]

I have this code to calculate levenshtein distance:

public static int CompareStrings(string string1, string string2)
{
    if (string.IsNullOrEmpty(string1) && string.IsNullOrEmpty(string2)) return 0;
    if (string.IsNullOrEmpty(string1)) return string2.Length;
    if (string.IsNullOrEmpty(string2)) return string1.Length;

    if (string1.Length > string2.Length)
    {
        string temp = string1;

        string1 = string2;
        string2 = temp;
    }

    var distances = new int[string1.Length + 1, string2.Length + 1];
    for (int i = 0; i <= string1.Length; i++)
    {
        for (int j = 1; i <= string2.Length; j++)
        {
            int a = Math.Min(distances[i - 1, j] + 1, distances[i, j - 1] + 1);
            int b = string2[j - 1] == string1[i - 1] ? 0 : 1;

            distances[i, j] = Math.Min(a, b);
        }
    }

    return distances[string1.Length, string2.Length];
}

public static int CompareStrings(string string1, string string2)
{
    if (string.IsNullOrEmpty(string1) && string.IsNullOrEmpty(string2)) return 0;
    if (string.IsNullOrEmpty(string1)) return string2.Length;
    if (string.IsNullOrEmpty(string2)) return string1.Length;

    if (string1.Length > string2.Length)
    {
        string temp = string1;

        string1 = string2;
        string2 = temp;
    }

    var distances = new int[string1.Length + 1, string2.Length + 1];
    for (int i = 0; i <= string1.Length; i++)
    {
        for (int j = 1; i <= string2.Length; j++)
        {
            int a = Math.Min(distances[i - 1, j] + 1, distances[i, j - 1] + 1);
            int b = string2[j - 1] == string1[i - 1] ? 0 : 1;

            distances[i, j] = Math.Min(a, b);
        }
    }

    return distances[string1.Length, string2.Length];
}

When string1 is empty and string2 is "Example", it works. When string1 is "Ex" and string2 is "Example", it throws an IndexOutOfRangeException.

21 Replies

canton7•3y ago

Which line throws the exception?

BujjuOP•3y ago

I don't remember how to find that

canton7•3y ago

VS should highlight the line in yellow when the exception is thrown. It will also be in the stack trace

BujjuOP•3y ago

It doesn't highlight it in yellow, but it shows up in the Debug output

canton7•3y ago

What exactly do you see in the debug output?

BujjuOP•3y ago

Exception thrown: 'System.IndexOutOfRangeException' in RainBOT.dll

canton7•3y ago

Is something higher up catching the exception?

BujjuOP•3y ago

The method is being run in an async task if that could be causing the issue

canton7•3y ago

I'm guessing it's not being awaited?

BujjuOP•3y ago

public Task<IEnumerable<DiscordAutoCompleteChoice>> Provider(AutocompleteContext ctx) =>
    Task.FromResult(myList.OrderBy(x => Utilities.CompareStrings((string)ctx.OptionValue, x.Name)));

public Task<IEnumerable<DiscordAutoCompleteChoice>> Provider(AutocompleteContext ctx) =>
    Task.FromResult(myList.OrderBy(x => Utilities.CompareStrings((string)ctx.OptionValue, x.Name)));

canton7•3y ago

Debug -> Windows -> Exception Settings, change the little checkbox next to "Common Language Exceptions" from grey to a tick. Don't get confused by "C++ Exceptions" or "Win32 Exceptions"

canton7•3y ago

(when you're done here, set it back with this button: )