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有人能发现我的Damerau Levenshtein远程实现中的错误吗?

Amy · 技术社区 · 14 年前

我试过摆弄数组边界,但那只会导致 IndexOutOfRangeExceptions

public static class FuzzyStringMatcher
{
    private const int DELETION = 0;
    private const int INSERTION = 1;
    private const int SUBSTITUTION = 2;
    private const int TRANSPOSITION = 3;

    private const int COST_OF_DELETION = 1;
    private const int COST_OF_INSERTION = 1;
    private const int COST_OF_TRANSPOSITION = 1;
    private const int COST_OF_SUBSTITUTION = 1;

    public static int Compute_DamerauLevenshtein_Distance(string a, string b)
    {
        int[,] rows = new int[a.Length + 1, b.Length + 1];
        int cost_ratio;
        int[] calculations = new int[4];

        //
        // Init the array
        //
        for (int i = 0; i < rows.GetUpperBound(0); i++)
            rows[i, 0] = i;

        for (int i = 0; i < rows.GetUpperBound(1); i++)
            rows[0, i] = i;


        for (int aidx = 1; aidx < rows.GetUpperBound(0); aidx++)
        {
            for (int bidx = 1; bidx < rows.GetUpperBound(1); bidx++)
            {
                if (a[aidx - 1] == b[bidx - 1])
                    cost_ratio = 0;
                else
                    cost_ratio = 1;

                calculations[DELETION] = rows[aidx - 1, bidx] + COST_OF_DELETION;
                calculations[INSERTION] = rows[aidx, bidx - 1] + COST_OF_INSERTION;
                calculations[SUBSTITUTION] = rows[aidx - 1, bidx - 1] + cost_ratio * COST_OF_SUBSTITUTION;
                calculations[TRANSPOSITION] = int.MaxValue;

                if (aidx > 1 && bidx > 1 && a[aidx] == b[bidx - 1] && a[aidx - 1] == b[bidx])
                    calculations[TRANSPOSITION] = rows[aidx - 2, bidx - 2] + cost_ratio * COST_OF_TRANSPOSITION;

                rows[aidx, bidx] = calculations.Min();
            }
        }

        int score = rows[rows.GetUpperBound(0) - 1, rows.GetUpperBound(1) - 1];
        if (a.Contains(b) || b.Contains(a))
            score = score / 2;
        return score;
    }
}

我的实现基于上的Wikipedia页面中给出的算法 Damerau-Levenshtein-Distance

2 回复 | 直到 14 年前

Peter Mortensen icecrime 9 年前

维基百科文章中没有:

if (a.Contains(b) || b.Contains(a))
        score = score / 2;

因为你的例子是这样的——整数除法是1/2==0,那么可能就是这样。

max 14 年前

+1给卢·佛朗哥。但除此之外,似乎还有很多索引问题(请注意,所有4个 for

    public static int Compute_DamerauLevenshtein_Distance2(string a, string b)
    {
        int[,] rows = new int[a.Length + 1, b.Length + 1];
        int cost_ratio;
        int[] calculations = new int[4];

        for(int i = 0; i <= rows.GetUpperBound(0); i++)
            rows[i, 0] = i;

        for(int i = 1; i <= rows.GetUpperBound(1); i++)
            rows[0, i] = i;


        for(int aidx = 1; aidx <= rows.GetUpperBound(0); aidx++)
        {
            for(int bidx = 1; bidx <= rows.GetUpperBound(1); bidx++)
            {
                if(a[aidx - 1] == b[bidx - 1])
                    cost_ratio = 0;
                else
                    cost_ratio = 1;

                calculations[DELETION] = rows[aidx - 1, bidx] + COST_OF_DELETION;
                calculations[INSERTION] = rows[aidx, bidx - 1] + COST_OF_INSERTION;
                calculations[SUBSTITUTION] = rows[aidx - 1, bidx - 1] + cost_ratio * COST_OF_SUBSTITUTION;
                calculations[TRANSPOSITION] = int.MaxValue;

                if(aidx > 1 && bidx > 1 && a[aidx - 1] == b[bidx - 2] && a[aidx - 2] == b[bidx - 1])
                    calculations[TRANSPOSITION] = rows[aidx - 2, bidx - 2] + cost_ratio * COST_OF_TRANSPOSITION;

                rows[aidx, bidx] = calculations.Min();
            }
        }

        int score = rows[rows.GetUpperBound(0), rows.GetUpperBound(1)];
        return score;
    }