C# 中寻找最大值的最佳数据结构？

Question

I need to know which is the best data structure for finding a maximal value and is it implemented in C#? For now I'm using SortedDictioniry but it sorts the keys and basically I don't need the keys to be sorted but what I need is a faster way to find the maximal value. Also after I find the maximal value I need the key or the index corresponding to this value. Also if it is possible to have a quick insertion and quick removal of the elements, hopefully not more than O(log n). Is there such a structure and how can I use it? Thank you!

Answer 1

That sounds just like a max-heap , there's plenty of on-line information on how to implement one from scratch (it isn't part of C# standard data structures).

For instance, take a look at this implementation , complete with a detailed explanation.

Answer 2

The most efficient will be max-heap, as previously stated. It is not a part of .Net, but you can choose from 3rd party libraries, like IntervalHeap (from http://www.itu.dk/research/c5/ )

Answer 3

You could use a SortedList<TKey, TValue> or a SortedDictionary<TKey, TValue> (as you already do). Another suitable collection type would be the Max-Heap; however, the .NET class library does not include one.

See also SortedList and SortedDictionary Collection Types for a comparison on MSDN. Also I don't see another possibility than sorting in some way by the key, if you want too have a fast access time on the maximum value.

Answer 4

As of .NET 6, the most suitable data structure for this scenario is probably the PriorityQueue<TElement, TPriority> class. This container supports only the operations Enqueue , Dequeue and Peek , with the smaller priority elements dequeued first. Elements with equal priority are dequeued with undefined order. To make it deque first the elements with the largest priority you need to supply it with a custom IComparer<T> , like the one below:

class ReverseComparer<T> : IComparer<T>
{
    public int Compare(T x, T y) => -Comparer<T>.Default.Compare(x, y);
}

Usage example, with priority of type int and elements of type string :

var queue = new PriorityQueue<string, int>(new ReverseComparer<int>());
queue.Enqueue("Red", 10);
queue.Enqueue("Green", 20);
queue.Enqueue("Yellow", 15);
queue.Enqueue("Brown", 25);
queue.Enqueue("Purple", 20);
while (queue.TryDequeue(out var element, out var priority))
{
    Console.WriteLine($"{priority} -> {element}");
}

Output:

25 -> Brown
20 -> Purple
20 -> Green
15 -> Yellow
10 -> Red

Online demo .