-
慕仙森
好的，这是多个双向版本：using System;using System.Collections.Generic;using System.Text;class BiDictionary<TFirst, TSecond>{
IDictionary<TFirst, IList<TSecond>> firstToSecond = new Dictionary<TFirst, IList<TSecond>>();
IDictionary<TSecond, IList<TFirst>> secondToFirst = new Dictionary<TSecond, IList<TFirst>>();
private static IList<TFirst> EmptyFirstList = new TFirst[0];
private static IList<TSecond> EmptySecondList = new TSecond[0];
public void Add(TFirst first, TSecond second)
{
IList<TFirst> firsts;
IList<TSecond> seconds;
if (!firstToSecond.TryGetValue(first, out seconds))
{
seconds = new List<TSecond>();
firstToSecond[first] = seconds;
}
if (!secondToFirst.TryGetValue(second, out firsts))
{
firsts = new List<TFirst>();
secondToFirst[second] = firsts;
}
seconds.Add(second);
firsts.Add(first);
}
// Note potential ambiguity using indexers (e.g. mapping from int to int)
// Hence the methods as well...
public IList<TSecond> this[TFirst first]
{
get { return GetByFirst(first); }
}
public IList<TFirst> this[TSecond second]
{
get { return GetBySecond(second); }
}
public IList<TSecond> GetByFirst(TFirst first)
{
IList<TSecond> list;
if (!firstToSecond.TryGetValue(first, out list))
{
return EmptySecondList;
}
return new List<TSecond>(list); // Create a copy for sanity
}
public IList<TFirst> GetBySecond(TSecond second)
{
IList<TFirst> list;
if (!secondToFirst.TryGetValue(second, out list))
{
return EmptyFirstList;
}
return new List<TFirst>(list); // Create a copy for sanity
}}class Test{
static void Main()
{
BiDictionary<int, string> greek = new BiDictionary<int, string>();
greek.Add(1, "Alpha");
greek.Add(2, "Beta");
greek.Add(5, "Beta");
ShowEntries(greek, "Alpha");
ShowEntries(greek, "Beta");
ShowEntries(greek, "Gamma");
}
static void ShowEntries(BiDictionary<int, string> dict, string key)
{
IList<int> values = dict[key];
StringBuilder builder = new StringBuilder();
foreach (int value in values)
{
if (builder.Length != 0)
{
builder.Append(", ");
}
builder.Append(value);
}
Console.WriteLine("{0}: [{1}]", key, builder);
}}
-
白衣非少年
正如其他人所说，字典中没有从值到键的映射。我刚刚注意到您想要从Value映射到多个键-我把这个解决方案留给单个值版本，但是接下来我将为多条目双向映射添加另一个答案。这里通常采用的方法是有两本字典-一种是映射方式，另一种是映射方式。将它们封装在一个单独的类中，并计算出当您拥有重复的键或值时要做什么(例如抛出异常、覆盖现有条目或忽略新条目)。就我个人而言，我可能会选择抛出一个例外-它使成功行为更容易定义。就像这样：using System;using System.Collections.Generic;class BiDictionary<TFirst, TSecond>{
IDictionary<TFirst, TSecond> firstToSecond = new Dictionary<TFirst, TSecond>();
IDictionary<TSecond, TFirst> secondToFirst = new Dictionary<TSecond, TFirst>();
public void Add(TFirst first, TSecond second)
{
if (firstToSecond.ContainsKey(first) ||
secondToFirst.ContainsKey(second))
{
throw new ArgumentException("Duplicate first or second");
}
firstToSecond.Add(first, second);
secondToFirst.Add(second, first);
}
public bool TryGetByFirst(TFirst first, out TSecond second)
{
return firstToSecond.TryGetValue(first, out second);
}
public bool TryGetBySecond(TSecond second, out TFirst first)
{
return secondToFirst.TryGetValue(second, out first);
}}class Test{
static void Main()
{
BiDictionary<int, string> greek = new BiDictionary<int, string>();
greek.Add(1, "Alpha");
greek.Add(2, "Beta");
int x;
greek.TryGetBySecond("Beta", out x);
Console.WriteLine(x);
}}
-
MM们
字典并不是真正像这样工作的，因为虽然键的唯一性得到了保证，但是值的唯一性却不是这样的。var greek = new Dictionary<int, string> { { 1, "Alpha" }, { 2, "Alpha" } };你希望得到什么greek.WhatDoIPutHere("Alpha")?因此，您不能期望将这样的内容滚到框架中。您需要自己的方法来实现自己的独特用途-您想返回一个数组(或IEnumerable<T>)?如果存在具有给定值的多个键，是否要抛出异常？如果没有呢？就我个人而言，我会选择一个可列举的，如下所示：IEnumerable<TKey> KeysFromValue<TKey, TValue>(this Dictionary<TKey, TValue> dict, TValue val){
if (dict == null)
{
throw new ArgumentNullException("dict");
}
return dict.Keys.Where(k => dict[k] == val);}var keys = greek.KeysFromValue("Beta");
int exceptionIfNotExactlyOne = greek.KeysFromValue("Beta").Single();