（一）算法

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项目地址

• 教程作者：
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• 代码仓库地址：

• 所用到的框架和插件：

dbt 
airflow

一、题目

1.1 基础题

1. 反转字符串

输入 “hello”，输出 “olleh”。
要求：不能直接用 Array.Reverse。

string ReverseString(string input)
{if (string.IsNullOrEmpty(input)) return input;char[] arr = input.ToCharArray();int left = 0, right = arr.Length - 1;while (left < right){(arr[left], arr[right]) = (arr[right], arr[left]);left++;right--;}return new string(arr);
}

2. 判断回文字符串

输入 “abba” 返回 true，输入 “abc” 返回 false。

bool IsPalindrome(string input)
{if (string.IsNullOrEmpty(input)) return true;int left = 0, right = input.Length - 1;while (left < right){while (left < right && !char.IsLetterOrDigit(input[left])) left++;while (left < right && !char.IsLetterOrDigit(input[right])) right--;if (char.ToLower(input[left]) != char.ToLower(input[right]))return false;left++;right--;}return true;
}

3. 两个数组的交集

输入 nums1 = [1,2,2,1]，nums2 = [2,2] → 输出 [2,2]。

int[] Intersect(int[] nums1, int[] nums2)
{var dict = new Dictionary<int, int>();foreach (var n in nums1){if (!dict.ContainsKey(n)) dict[n] = 0;dict[n]++;}var result = new List<int>();foreach (var n in nums2){if (dict.ContainsKey(n) && dict[n] > 0){result.Add(n);dict[n]--;}}return result.ToArray();
}

4. 字符串中第一个不重复的字符

输入 “leetcode” → 输出 l
输入 “aabb” → 输出 null 或特殊符号。

char? FirstUniqueChar(string s)
{var dict = new Dictionary<char, int>();foreach (var ch in s){if (!dict.ContainsKey(ch)) dict[ch] = 0;dict[ch]++;}foreach (var ch in s){if (dict[ch] == 1) return ch;}return null;
}

5. LRU 缓存机制 (经典 OOD 题)

要求：
Get O(1)
Put O(1)
超出容量时移除最近最少使用的元素。

public class LRUCache
{private readonly int _capacity;private readonly Dictionary<int, LinkedListNode<(int Key, int Value)>> _cache;private readonly LinkedList<(int Key, int Value)> _list;public LRUCache(int capacity){_capacity = capacity;_cache = new Dictionary<int, LinkedListNode<(int, int)>>();_list = new LinkedList<(int, int)>();}public int Get(int key){if (!_cache.TryGetValue(key, out var node))return -1;_list.Remove(node);_list.AddFirst(node);return node.Value.Value;}public void Put(int key, int value){if (_cache.TryGetValue(key, out var node)){_list.Remove(node);}else if (_cache.Count >= _capacity){var last = _list.Last;if (last != null){_cache.Remove(last.Value.Key);_list.RemoveLast();}}var newNode = new LinkedListNode<(int, int)>((key, value));_list.AddFirst(newNode);_cache[key] = newNode;}
}

6. 写一个线程安全的 有界队列

public class BlockingQueue<T>
{private readonly Queue<T> _queue = new();private readonly int _capacity;private readonly object _lock = new();public BlockingQueue(int capacity) => _capacity = capacity;public void Enqueue(T item){lock (_lock){while (_queue.Count >= _capacity)Monitor.Wait(_lock);_queue.Enqueue(item);Monitor.PulseAll(_lock);}}public T Dequeue(){lock (_lock){while (_queue.Count == 0)Monitor.Wait(_lock);var item = _queue.Dequeue();Monitor.PulseAll(_lock);return item;}}
}

7. 实现一个 LINQ 的 Where 扩展方法

• 模拟实现 IEnumerable.Where

public static class MyLinqExtensions
{public static IEnumerable<T> MyWhere<T>(this IEnumerable<T> source,Func<T, bool> predicate){foreach (var item in source){if (predicate(item))yield return item;}}
}

8. 并发请求控制

写一个方法，接收一组 Func，限制同时最多执行 N 个任务，直到全部完成。

public async Task RunWithMaxConcurrency(IEnumerable<Func<Task>> tasks, int maxConcurrency)
{using SemaphoreSlim semaphore = new(maxConcurrency);var runningTasks = tasks.Select(async task =>{await semaphore.WaitAsync();try{await task();}finally{semaphore.Release();}});await Task.WhenAll(runningTasks);
}

9. 设计 TinyUrl 系统

输入长链接 “https://example.com/abc/def”
输出短链接 “http://tinyurl.com/xyz123”
要求短链接能还原为长链接。

public class TinyUrlService
{private readonly Dictionary<string, string> _map = new();private readonly string _baseUrl = "http://tinyurl.com/";private readonly Random _random = new();public string Encode(string longUrl){var key = Guid.NewGuid().ToString("N").Substring(0, 6);_map[key] = longUrl;return _baseUrl + key;}public string Decode(string shortUrl){var key = shortUrl.Replace(_baseUrl, "");return _map[key];}
}