[#3005] feat(leetcode): init project, add C# solution

problems/3005-count_elements_with_maximum_frequency/csharp/Program.cs

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+// LeetCode 3005: Count_elements_with_maximum_frequency
+// 難度: Easy
+// 日期: 2025-09-22
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+public class Solution {
+    public int MaxFrequencyElements(int[] nums)
+    {
+        Dictionary<int, int> frequencyMap = new Dictionary<int, int>();
+
+        // put nums into dictionary map
+        foreach (var num in nums)
+        {
+            if (!frequencyMap.ContainsKey(num))
+            {
+                frequencyMap.Add(num, 0);
+            }
+            frequencyMap[num]++;
+        }
+
+        // find most frequency nums
+        int maxFrequency = 0;
+        if (frequencyMap.Count != 0)
+        {
+            maxFrequency = frequencyMap.Values.Max();
+        }
+
+        // count if have same max frequency nus
+        int count = 0;
+        foreach (var dic in frequencyMap)
+        {
+            if (dic.Value == maxFrequency)
+            {
+                count += maxFrequency;
+            }
+        }
+
+        return count;
+    }
+}
+
+public class Program {
+    public static void Main() {
+        var s = new Solution();
+        // TODO: 可加入簡單輸入/輸出測試
+        Console.WriteLine("Hello LeetCode 3005!");
+    }
+}
+