记一次面试题

参加了一次 黑客排名 的技术面试

得到的经验就是别去看那有的没的的题干，很浪费时间，而是要：

1. 看示例输入
2. 看示例输出
3. 找输入输出的关系
4. 写框架代码
5. 找题中的细节要求
6. 完善代码
7. Test & Debug

我有 70 分钟作答 ，但是吧，这题弱智都做得出来，无非是时间问题

算法题

从 List<List<int>> 中找出最大相邻相同数字的方阵长度，比如

输入

1 1 1
1 1 0
1 0 1

输出 2

解

本题需要用到 动态规划 的思想

二维数组 dp 来记录以每个元素为右下角的最大相邻相同数字的方阵长度
然后遍历输入的矩阵，根据当前元素的值来更新 dp
最后，返回 dp 中的最大值作为最大相邻相同数字的方阵长度

static int FindMaxSquareLength(List<List<int>> matrix) {
    var rows = matrix.Count;
    var cols = matrix[0].Count;
    var maxLength = 0;

    var dp = new int[rows, cols];

    for (var i = 0; i < rows; i++)
    for (var j = 0; j < cols; j++) {
        if (i == 0 || j == 0)
            dp[i, j] = matrix[i][j];
        else if (matrix[i][j] == 1)
            dp[i, j] = Math.Min(dp[i - 1, j - 1], Math.Min(dp[i - 1, j], dp[i, j - 1])) + 1;

        maxLength = Math.Max(maxLength, dp[i, j]);
    }

    return maxLength;
}

List<List<int>> matrix = new() {
    new() { 1, 1, 1 },
    new() { 1, 1, 0 },
    new() { 1, 0, 1 }
};

var maxLength = FindMaxSquareLength(matrix);
Console.WriteLine("最大相邻相同数字的方阵长度为: " + maxLength);

技能题

编写一个 HTTP GET 查询

URL: https://jsonmock.hackerrank.com/api/transactions
它不提供除了 ?page=num 以外的查询参数

编写代码以实现

List<string> maximumTransfer(string name, string city)

其中，找出最大的 credit 为 [0]，最大的 debit 为 [1]

解

这个真没啥好说的，单纯考基本功

static async Task<List<string>> maximumTransfer(string name, string city) {
    var result = new List<string>();
    var allData = await GetAllData();

    var maxCredit = decimal.MinValue;
    var maxDebit = decimal.MinValue;

    var maxCreditAmount = "";
    var maxDebitAmount = "";

    foreach (var data in allData.Where(data => data.userName == name && data.location.city == city))
        switch (data.txnType) {
            case "credit": {
                var creditAmount = ParseAmount(data.amount);
                if (creditAmount > maxCredit) {
                    maxCredit = creditAmount;
                    maxCreditAmount = data.amount;
                }

                break;
            }
            case "debit": {
                var debitAmount = ParseAmount(data.amount);
                if (debitAmount > maxDebit) {
                    maxDebit = debitAmount;
                    maxDebitAmount = data.amount;
                }

                break;
            }
        }

    result.Add(maxCreditAmount);
    result.Add(maxDebitAmount);

    return result;
}

static async Task<List<Data>> GetAllData() {
    var allData = new List<Data>();
    var currentPage = 1;
    var totalPages = 1;

    while (currentPage <= totalPages) {
        var url = $"https://jsonmock.hackerrank.com/api/transactions?page={currentPage}";
        using (var client = new HttpClient()) {
            var response = await client.GetAsync(url);
            if (response.IsSuccessStatusCode) {
                var json = await response.Content.ReadAsStringAsync();
                Root root = JsonConvert.DeserializeObject<Root>(json);
                allData.AddRange(root.data);
                totalPages = root.total_pages;
            } else
                throw new($"Failed to retrieve data from {url}. Status code: {response.StatusCode}");
        }

        currentPage++;
    }

    return allData;
}

static decimal ParseAmount(string amount) {
    var cleanedAmount = amount.Replace("$", "").Replace(",", "");
    return decimal.Parse(cleanedAmount);
}

var maxTransfer = await maximumTransfer("John Doe", "New York");
Console.WriteLine("Max Credit: " + maxTransfer[0]);
Console.WriteLine("Max Debit: " + maxTransfer[1]);

internal class Data {
    public int id { get; set; }
    public int userId { get; set; }
    public string userName { get; set; }
    public object timestamp { get; set; }
    public string txnType { get; set; }
    public string amount { get; set; }
    public Location location { get; set; }
    public string ip { get; set; }
}

internal class Location {
    public int id { get; set; }
    public string address { get; set; }
    public string city { get; set; }
    public int zipCode { get; set; }
}

internal class Root {
    public int page { get; set; }
    public int per_page { get; set; }
    public int total { get; set; }
    public int total_pages { get; set; }
    public List<Data> data { get; set; }
}

SQL 题

写一个 SQL 查询，有表

customers(id: smallint, name:varchar)
warehouses(customer_id, volume: decimal, is_active:smallint)

期望输出

record(name, warehouses, min_volume, max_volume, total_volume)

只有 active 的仓库才被列出，按 name 排序

解

或许 ChatGPT 写的比你更快更好 ，有的时候找找自己原因，好吧，这么多年了工资涨没涨，有没有认真工作，好不，这么多年都是这个代码质量我真的疯掉了。

SELECT
  c.name AS name,
  COUNT(w.customer_id) AS warehouses,
  MIN(w.volume) AS min_volume,
  MAX(w.volume) AS max_volume,
  SUM(w.volume) AS total_volume
FROM
  customers c
  INNER JOIN warehouses w ON c.id = w.customer_id
WHERE
  w.is_active = 1
GROUP BY
  c.id, c.name
ORDER BY
  c.name;