[#1792]feat(MaxAverageRatio) : add C# brute force solution

problems/1792-maximum-average-pass-ratio/README.md

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+# [1792] Maximum Average Pass Ratio
+
+## 題目資訊
+- **難度**: Medium
+- **標籤**: Array, Greedy, Heap(Priority Queue)
+- **題目連結**: [LeetCode](https://leetcode.com/problems/maximum-average-pass-ratio/)
+- **練習日期**: 2025-09-01
+
+## 題目描述
+There is a school that has classes of students and each class will be having a final exam. You are given a 2D integer array `classes`, where `classes[i] = [passi, totali]`. You know beforehand that in the `ith` class, there are `totali` total students, but only `passi` number of students will pass the exam.
+
+You are also given an integer `extraStudents`. There are another `extraStudents` brilliant students that are **guaranteed** to pass the exam of any class they are assigned to. You want to assign each of the `extraStudents` students to a class in a way that **maximizes** the **average** pass ratio across **all** the classes.
+
+The **pass ratio** of a class is equal to the number of students of the class that will pass the exam divided by the total number of students of the class. The **average pass ratio** is the sum of pass ratios of all the classes divided by the number of the classes.
+
+Return the *maximum* possible average pass ratio after assigning the `extraStudents` students. Answers within `10-5` of the actual answer will be accepted.
+
+## 解題思路
+
+### 初步分析
+- 這題主要考察什麼概念?
+   - 貪心算法，找出每次分配學生，通過率可以提升至最高
+- Pass Ratio = pass / total
+- Average Pass Ratio = sum of pass ration / number of class
+
+### 解法概述
+1. **暴力解法**: 
+   - 思路：
+      - 每次分配一個學生看哪個班級提升率會最高
+      - leetcode 這邊會 time limit exceeded
+   - 時間複雜度：O(N)
+   - 空間複雜度：O(N)
+   
+2. **最佳解法**: 
+   - 思路：
+      - Priority Queue(Max Heap) 存每個班級淺在
+   - 時間複雜度：O(?)
+   - 空間複雜度：O(?)
+
+## 測試案例
+
+### 範例輸入輸出
+```
+Input: classes = [[1,2],[3,5],[2,2]], extraStudents = 2
+Output: 0.78333
+Explanation: You can assign the two extra students to the first class. The average pass ratio will be equal to (3/4 + 3/5 + 2/2) / 3 = 0.78333.
+```
+
+### 邊界情況
+- 1 <= classes.length <= 10^5
+- classes[i].length == 2
+- 1 <= passi <= totali <= 10^5
+- 1 <= extraStudents <= 10^5
+
+## 學習筆記
+
+### 今天學到什麼？
+- 
+
+### 遇到的困難
+- 
+
+### 改善方向
+- 
+
+### 相關題目
+- [題目編號] 題目名稱 - 相似概念
+- [題目編號] 題目名稱 - 進階版本
+
+---
+**總結**: 這題的核心概念是...，適合練習...技巧。

problems/1792-maximum-average-pass-ratio/csharp/Program.cs

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+// LeetCode 1792: Maximum Average Pass Ratio
+// 難度: Medium
+// 日期: 2025-09-01
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+public class Solution {
+    public double MaxAverageRatioByBruteForce(int[][] classes, int extraStudents)
+    {
+        var n = classes.Length;
+        var pass = new int[n];
+        var total = new int[n];
+
+        for (var i = 0; i < n; i++)
+        {
+            pass[i] = classes[i][0];
+            total[i] = classes[i][1];
+        }
+
+        for (int student = 0; student < extraStudents; student++)
+        {
+            int bestClass = -1;
+            double maxInprovement = 0;
+
+            for (int i = 0; i < n; i++)
+            {
+                double currentAvg = CalculateAvergaeRatio(pass, total);
+
+                pass[i]++;
+                total[i]++;
+
+                double newAvg = CalculateAvergaeRatio(pass, total);
+                double improvement = newAvg - currentAvg;
+
+                pass[i]--;
+                total[i]--;
+
+                if (improvement > maxInprovement)
+                {
+                    maxInprovement = improvement;
+                    bestClass = i;
+                }
+            }
+
+            if (bestClass != -1)
+            {
+                pass[bestClass]++;
+                total[bestClass]++;
+            }
+        }
+
+        return CalculateAvergaeRatio(pass, total);
+    }
+
+    private double CalculateAvergaeRatio(int[] pass, int[] total) {
+        double sum = 0;
+        for (var i = 0; i < pass.Length; i++)
+        {
+            sum += (double)pass[i] / total[i];
+        }
+        return sum / pass.Length;
+    }
+}
+
+// 測試程式
+public class Program
+{
+    public static void Main()
+    {
+        Solution solution = new Solution();
+
+        // TestCase
+        TestCase1(solution);
+        TestCase2(solution);
+    }
+
+    static void TestCase1(Solution solution)
+    {
+        // Input: 
+        int[][] classes = new int[][]
+        {
+            new int[] {1, 2},
+            new int[] {3, 5},
+            new int[] {2, 2}
+        };
+        int extraStudents = 2;
+
+        Console.WriteLine("Test 1: ");
+        Console.WriteLine($"classes: [{string.Join("], [", classes.Select(c => string.Join(", ", c)))}]");
+        Console.WriteLine($"extraStudents: {extraStudents}");
+
+        // Expected: 
+        Console.WriteLine("Expect: ");
+        Console.WriteLine($"output: 0.78333");
+
+        // Actual: 
+        Console.WriteLine("Actual: ");
+        Console.WriteLine($"Brute Force: {solution.MaxAverageRatioByBruteForce(classes, extraStudents):F6}");
+        //Console.WriteLine($"output: {solution.MaxAverageRatio(classes, extraStudents):F6}");
+    }
+
+
+    static void TestCase2(Solution solution)
+    {
+        // Input: 
+        int[][] classes = new int[][]
+        {
+            new int[] {2, 4},
+            new int[] {3, 9},
+            new int[] {4, 5},
+            new int[] {2, 10}
+        };
+        int extraStudents = 4;
+
+        Console.WriteLine("Test 2: ");
+        Console.WriteLine($"classes: [{string.Join("], [", classes.Select(c => string.Join(", ", c)))}]");
+        Console.WriteLine($"extraStudents: {extraStudents}");
+
+        // Expected: 
+        Console.WriteLine("Expect: ");
+        Console.WriteLine($"output: 0.53485");
+
+        // Actual: 
+        Console.WriteLine("Actual: ");
+        Console.WriteLine($"Brute Force: {solution.MaxAverageRatioByBruteForce(classes, extraStudents):F6}");
+        //Console.WriteLine($"output: {solution.MaxAverageRatio(classes, extraStudents):F6}");
+    }
+}

problems/1792-maximum-average-pass-ratio/csharp/csharp.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>