entries用于存储当前每个节点的数据，其中四个字段分别表示：
cs
hashCode：key对应的hash值
next：处理hash冲突，可以理解为是一个链表结构，邻接表
key：存储的key
value：存储的valuebuckets存储桶，用于存储hash映射
设计的巧妙之处在这个桶buckets，每个hashCode取模（当前size最近的大于size的素数），这里用素数是为了减少hash冲突的频率，key取hash再取模=index，就放入存储桶中，buckets[index]记录的是当前key对应的第一个entries的下标位置，entries不管是增加还是删除，会优先连续的放在数组中，举例删了index[2]的数据，这个时候加入一个数据，会无脑放在这个index[2]的位置，同理[.next]也维护了删除的单向链表的数据，所有删掉的index下标数据，也是存在链中等待新的数据插入，这里是反向链表获取index，所以可以理解为最早清理的index，最晚被用到。
具体可以看看代码
cs
using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.Diagnostics.Contracts;
using System.Runtime.Serialization;
using System.Security.Permissions;
using System.Text;
namespace DictionaryTest
{
public static class MHashHelpers
{
public const int MaxPrimeArrayLength = 0x7FEFFFFD;
public static readonly int[] primes = {
3, 7, 11, 17, 23, 29, 37, 47, 59, 71, 89, 107, 131, 163, 197, 239, 293, 353, 431, 521, 631, 761, 919,
1103, 1327, 1597, 1931, 2333, 2801, 3371, 4049, 4861, 5839, 7013, 8419, 10103, 12143, 14591,
17519, 21023, 25229, 30293, 36353, 43627, 52361, 62851, 75431, 90523, 108631, 130363, 156437,
187751, 225307, 270371, 324449, 389357, 467237, 560689, 672827, 807403, 968897, 1162687, 1395263,
1674319, 2009191, 2411033, 2893249, 3471899, 4166287, 4999559, 5999471, 7199369};
public static bool IsPrime(int candidate)
{
if ((candidate & 1) != 0)
{
int limit = (int)Math.Sqrt(candidate);
for (int divisor = 3; divisor <= limit; divisor += 2)
{
if ((candidate % divisor) == 0)
return false;
}
return true;
}
return (candidate == 2);
}
public static int GetPrime(int min)
{
for (int i = 0; i < primes.Length; i++)
{
int prime = primes[i];
if (prime >= min) return prime;
}
for (int i = (min | 1); i < Int32.MaxValue; i += 2)
{
if (IsPrime(i) && ((i - 1) % 101 != 0))
return i;
}
return min;
}
public static int ExpandPrime(int oldSize)
{
int newSize = 2 * oldSize;
// Allow the hashtables to grow to maximum possible size (~2G elements) before encoutering capacity overflow.
// Note that this check works even when _items.Length overflowed thanks to the (uint) cast
if ((uint)newSize > MaxPrimeArrayLength && MaxPrimeArrayLength > oldSize)
{
Contract.Assert(MaxPrimeArrayLength == GetPrime(MaxPrimeArrayLength), "Invalid MaxPrimeArrayLength");
return MaxPrimeArrayLength;
}
return GetPrime(newSize);
}
}
public class MDictionary<TKey, TValue>
{
private struct Entry
{
public int hashCode; // 存储 Key 对应的 hashCode
public int next; // 指向上一个存储的对象的index
public TKey key; // 存储的 Key
public TValue value; // 存储的 Value
}
private IEqualityComparer<TKey> comparer;
private int[] buckets; // 定长的存储桶
private Entry[] entries; // 定长的存储元素的数组
private int count; // 当前元素个数
private int freeList; // 删掉元素之后，还空余的位置，最新的一个，根据entries链表指向上一个
private int freeCount; // 空余的个数
public MDictionary() : this(0) { }
public MDictionary(int capacity)
{
if (capacity > 0)
{
Initialize(capacity);
}
this.comparer = EqualityComparer<TKey>.Default;
}
private void Initialize(int capacity)
{
int size = MHashHelpers.GetPrime(capacity);
buckets = new int[size];
entries = new Entry[size];
for (int i = 0; i < buckets.Length; i++)
{
buckets[i] = -1;
entries[i].hashCode = -1;
entries[i].next = -1;
entries[i].key = default(TKey);
entries[i].value = default(TValue);
}
count = 0;
freeList = -1;
freeCount = 0;
}
private void Resize()
{
Console.WriteLine($"[Resize]");
int newSize = MHashHelpers.ExpandPrime(count);
int[] newBuckets = new int[newSize];
for (int i = 0; i < newBuckets.Length; i++) newBuckets[i] = -1;
Entry[] newEntries = new Entry[newSize];
Array.Copy(entries, 0, newEntries, 0, count);
for (int i = 0; i < count; i++)
{
if (newEntries[i].hashCode != -1)
{
newEntries[i].hashCode = (comparer.GetHashCode(newEntries[i].key) & 0x7FFFFFFF);
}
}
for (int i = 0; i < count; i++)
{
if (newEntries[i].hashCode != -1)
{
int bucket = newEntries[i].hashCode % newSize;
newEntries[i].next = newBuckets[bucket];
newBuckets[bucket] = i;
}
}
buckets = newBuckets;
entries = newEntries;
PrintAll();
}
public void Insert(TKey key, TValue value)
{
Console.WriteLine($"[Insert] {key} {value}");
int hashCode = comparer.GetHashCode(key) & 0x7FFFFFFF;
int targetBucket = hashCode % buckets.Length;
for (int i = buckets[targetBucket]; i != -1; i = entries[i].next)
{
if (entries[i].hashCode == hashCode && comparer.Equals(entries[i].key, key))
{
entries[i].value = value;
PrintAll();
return;
}
}
int index;
if (freeCount > 0)
{
index = freeList;
freeList = entries[index].next;
freeCount--;
}
else
{
if (count == buckets.Length)
{
Resize();
targetBucket = hashCode % buckets.Length;
}
index = count;
count++;
}
entries[index].hashCode = hashCode;
entries[index].next = buckets[targetBucket];
entries[index].key = key;
entries[index].value = value;
buckets[targetBucket] = index;
PrintAll();
}
public bool Remove(TKey key)
{
Console.WriteLine($"[Remove] {key}");
int hashCode = comparer.GetHashCode(key) & 0x7FFFFFFF;
int bucket = hashCode % buckets.Length;
int last = -1;
for (int i = buckets[bucket]; i != -1; last = i, i = entries[i].next)
{
if (comparer.Equals(key, entries[i].key) && entries[i].hashCode == hashCode)
{
if (last == -1)
{
buckets[bucket] = entries[i].next;
}
else
{
entries[last].next = entries[i].next;
}
entries[i].hashCode = -1;
entries[i].next = -1;
entries[i].key = default(TKey);
entries[i].value = default(TValue);
freeList = i;
freeCount++;
PrintAll();
return true;
}
}
PrintAll();
return false;
}
public bool TryGetValue(TKey key, out TValue value)
{
Console.WriteLine($"[TryGetValue] {key}");
int hashCode = comparer.GetHashCode(key) & 0x7FFFFFFF;
int targetBucket = hashCode % buckets.Length;
for (int i = buckets[targetBucket]; i != -1; i = entries[i].next)
{
if (comparer.Equals(key, entries[i].key) && entries[i].hashCode == hashCode)
{
value = entries[i].value;
return true;
}
}
value = default(TValue);
return false;
}
public void Clear()
{
Console.WriteLine($"[Clear]");
if (count > 0)
{
for (int i = 0; i < buckets.Length; i++) buckets[i] = -1;
Array.Clear(entries, 0, count);
count = 0;
freeList = -1;
freeCount = 0;
}
PrintAll();
}
public void PrintAll()
{
Console.WriteLine($"[PrintAll]");
StringBuilder bucketInfo = new StringBuilder();
StringBuilder entriesInfo = new StringBuilder();
for (int i = 0; i < buckets.Length; i++)
{
bucketInfo.Append($"{i} [{buckets[i]}]").Append("\n");
}
Console.WriteLine("buckets: " + buckets.Length);
Console.Write(bucketInfo);
for (int i = 0; i < entries.Length; i++)
{
entriesInfo.Append($"{i} [{entries[i].hashCode}={entries[i].next}={entries[i].key}={entries[i].value}]").Append("\n");
}
Console.WriteLine("entries: " + entries.Length);
Console.Write(entriesInfo);
}
}
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Hello World!");
MDictionary<int, string> dict = new MDictionary<int, string>(2);
dict.Clear();
dict.Insert(0, "000");
dict.Insert(1, "111");
dict.Remove(0);
dict.Insert(2, "222");
dict.Insert(3, "333");
dict.Insert(4, "444");
dict.Remove(2);
dict.Insert(5, "555");
dict.Insert(6, "666");
dict.Remove(1);
dict.Insert(7, "777");
dict.Insert(14, "1414");
dict.Insert(21, "2121");
dict.Remove(14);
dict.Insert(28, "2828");
dict.Insert(35, "3535");
dict.Insert(42, "4242");
dict.Insert(55, "5555");
dict.Remove(21);
}
}
}一些参考：