查找整数列表中最小的缺失元素

问题描述

您好，

对于某些项目，我有一个字典，由整数键索引，可以分段（这就是为什么我没有使用一个列表）。例如，Keys集合可以包含{1,2,3,5,7}。

我有时必须在这个字典中插入一个元素，我想这样做，以便填充缺少的键。我想知道是否有一种方法使用Linq找到适当的索引来放置新值（在上面的例子中，表达式将返回4）。

任何想法？

谢谢，

Xavier

Hello,

For some project I have a dictionary, indexed by integer keys, that can be fragmented (which is why I did not use just a list). For example the Keys collection could contain {1, 2, 3, 5, 7}.

I sometimes have to insert an element in this dictionary, and I want to do it so it fills the missing keys. And I wondered if there was a way using Linq to find the appropriate index to put the new value at (in the above example, the expression would return 4).

Any ideas ?

Thanks,

Xavier

推荐答案

因为您只对第一个缺失的密钥感兴趣，解决方案是：

Because you are only interested in the first missing key, the solution is:

int[] keys = { 1, 2, 3, 5, 7 };

var arrayWithFirstMissingKey = keys
    .Select((key, index) => new { Key = key, Index = index })
    .Where(tuple => (tuple.Index + 1 < keys.Length) && (keys[tuple.Index + 1] > tuple.Key +1))
    .Select(tuple => tuple.Key +1)
    .Take(1)
    .ToArray();

第一个 选择创建（Key，Index）元组，因为Enumerables不支持索引， 

The 1st  Select creates (Key, Index) tuples, because Enumerables don't support indexes, 

Where子句检测到与其后继有间隙的第一个密钥。

The Where clause detects the first key which has a gap to it's successor.

第二个选择确定缺口的第一个缺失密钥。

The 2nd select determines the first missing key of the gap.

在找到第一个缺失密钥后，Take子句可以防止不必要的开销。

The Take clause prevents unnecessary overhead after the first missing key is found.

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