c# dictionary查找算法

C#中的`Dictionary`是基于哈希表实现的数据结构，因此查找操作的时间复杂度为O(1)。下面是一个示例代码：

using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        Dictionary<string, int> dict = new Dictionary<string, int>();
        dict.Add("apple", 1);
        dict.Add("banana", 2);
        dict.Add("orange", 3);

        if (dict.ContainsKey("apple"))
        {
            int value = dict["apple"];
            Console.WriteLine($"The value of 'apple' is {value}");
        }
        else
        {
            Console.WriteLine("The key 'apple' does not exist in the dictionary");
        }

        if (dict.ContainsKey("pear"))
        {
            int value = dict["pear"];
            Console.WriteLine($"The value of 'pear' is {value}");
        }
        else
        {
            Console.WriteLine("The key 'pear' does not exist in the dictionary");
        }
    }
}

输出结果为：

The value of 'apple' is 1
The key 'pear' does not exist in the dictionary

可以看到，通过`Dictionary`的`ContainsKey`方法和索引访问，可以快速判断一个键值是否存在，并获取对应的值。