获取项目序列的索引 [英] Getting the index of a sequence of items

问题描述

我试图获取 IEnumerable

var collection = new[] { 1, 2, 3, 4, 5 };
var sequence   = new[] { 2, 3 };

// IndexOf is an extension method.
collection.IndexOf(sequence); // Should return 1

我写了一个 IndexOf 扩展方法，并且它工作正常除非

I wrote an IndexOf extension method for this and it works fine unless there are more than one of the first item of the sequence in collection, consecutively:

// There are two items that are 2, consecutively in the collection,
// which is the first item of the sequence.
var collection = new[] { 1, 2, 2, 3, 4, 5 };
var sequence   = new[] { 2, 3 };

collection.IndexOf(sequence); // Should return 2 but returns -1

这里是 IndexOf 方法：

Here is the IndexOf method:

public static int IndexOf<T>(this IEnumerable<T> collection,
    IEnumerable<T> sequence)
{
    var comparer = EqualityComparer<T>.Default;
    var counter = 0;
    var index = 0;
    var seqEnumerator = sequence.GetEnumerator();

    foreach (var item in collection)
        if (seqEnumerator.MoveNext())
        {
            if (!comparer.Equals(item, seqEnumerator.Current))
            {
                seqEnumerator.Dispose();
                seqEnumerator = sequence.GetEnumerator();
                counter = 0;

                // UPDATED AFTER MICHAEL'S ANSWER,
                // IT WORKS WITH THIS ADDED PART:
                seqEnumerator.MoveNext();
                if (comparer.Equals(item, seqEnumerator.Current))
                    counter++;
            }
            else counter++;
            index++;
        }
        else break;

    var done = !seqEnumerator.MoveNext();
    seqEnumerator.Dispose();
    return done ? index - counter : -1;
}

我无法弄清楚如何解决这个问题。

I couldn't figure out how to fix this.

推荐答案

当你在第一个位置遇到错误符号时，重新启动序列迭代器，但是你不检查当前项是否匹配序列迭代器，所以你实际上从来没有比较第二2从收集到2从序列。

When you encounter wrong symbol on not first position you restarting the sequence iterator but you don't check if the current item is matching the start of the sequence iterator, so you actually never compare second 2 from collection to 2 from sequence .

这篇关于获取项目序列的索引的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！