首先,需要一個接口,用來獲取鍵以及獲取和設置值,如下所示:
namespace Skyiv.Util
{
interface IKeyValue<T, K, V>
{
K GetKey(T x);
V GetValue(T x);
void SetValue(T x, V v);
}
}
接著,就是我們的帶鍵值的優先隊列 KeyedPriorityQueue<T, K, V> 登場了:
using System;
using System.Collections.Generic;
namespace Skyiv.Util
{
class KeyedPriorityQueue<T, K, V>
{
IComparer<T> comparer;
IKeyValue<T, K, V> kver;
Dictionary<K, int> keys;
bool hasKey;
T[] heap;
public int Count { get; private set; }
public KeyedPriorityQueue(IKeyValue<T, K, V> kv) : this(null, kv) { }
public KeyedPriorityQueue(int capacity, IKeyValue<T, K, V> kv) : this(capacity, null, kv) { }
public KeyedPriorityQueue(IComparer<T> comparer, IKeyValue<T, K, V> kv) : this(16, comparer, kv) { }
public KeyedPriorityQueue(int capacity, IComparer<T> comparer, IKeyValue<T, K, V> kver)
{
this.keys = new Dictionary<K, int>();
this.comparer = (comparer == null) ? Comparer<T>.Default : comparer;
this.kver = kver;
this.hasKey = (kver != null);
this.heap = new T[capacity];
}
public bool ContainsKey(K key)
{
return keys.ContainsKey(key);
}
public void Update(T v)
{
if (!hasKey) throw new NotSupportedException();
if (typeof(T).IsValueType) throw new InvalidOperationException("T 不能是值類型");
if (!ContainsKey(kver.GetKey(v))) throw new ArgumentOutOfRangeException("v", v, "更新優先隊列時無此健值");
var id = keys[kver.GetKey(v)];
var cmp = comparer.Compare(v, heap[id]);
kver.SetValue(heap[id], kver.GetValue(v)); // 注意: 這一句要求 T 是引用類型,不能是值類型
if (cmp < 0) SiftDown(id);
else if (cmp > 0) SiftUp(id);
}
public void Push(T v)
{
if (Count >= heap.Length) Array.Resize(ref heap, Count * 2);
if (hasKey) keys[kver.GetKey(v)] = Count;
heap[Count] = v;
SiftUp(Count++);
}
public T Pop()
{
var v = Top();
if (hasKey) keys.Remove(kver.GetKey(v));
heap[0] = heap[--Count];
if (Count > 0) SiftDown(hasKey ? (keys[kver.GetKey(heap[0])] = 0) : 0);
return v;
}
public T Top()
{
if (Count > 0) return heap[0];
throw new InvalidOperationException("優先隊列為空");
}
void SiftUp(int n)
{
var v = heap[n];
for (var n2 = n / 2; n > 0 && comparer.Compare(v, heap[n2]) > 0; n = n2, n2 /= 2)
heap[hasKey ? (keys[kver.GetKey(heap[n2])] = n) : n] = heap[n2];
heap[hasKey ? (keys[kver.GetKey(v)] = n) : n] = v;
}
void SiftDown(int n)
{
var v = heap[n];
for (var n2 = n * 2; n2 < Count; n = n2, n2 *= 2)
{
if (n2 + 1 < Count && comparer.Compare(heap[n2 + 1], heap[n2]) > 0) n2++;
if (comparer.Compare(v, heap[n2]) >= 0) break;
heap[hasKey ? (keys[kver.GetKey(heap[n2])] = n) : n] = heap[n2];
}
heap[hasKey ? (keys[kver.GetKey(v)] = n) : n] = v;
}
}
}