列表中C#计数的动态出现次数

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        List<int> numbers = new List<int> { 1, 2, 3, 2, 1, 3, 4, 5, 2, 1, 3 };

        Dictionary<int, int> countDict = new Dictionary<int, int>();

        foreach (int num in numbers)
        {
            if (countDict.ContainsKey(num))
            {
                countDict[num]++;
            }
            else
            {
                countDict[num] = 1;
            }
        }

        foreach (KeyValuePair<int, int> pair in countDict)
        {
            Console.WriteLine("元素 {0} 出现了 {1} 次", pair.Key, pair.Value);
        }
    }
}