Question

我正在尝试在程序中实现二进制搜索算法，但似乎无法正常工作。

这是我的代码：

public static void Search(float[] array, float key)
    {
        int min = 0; 
        int max = array.Length - 1;
        int mid = 0;

        do
        {
            mid = (min + max) / 2;

            if (key > array[mid])
            {
                min = mid + 1; 
            }

            if (key < array[mid])
            {
                max = mid - 1; 
            }

            if (key == array[mid])
                Console.WriteLine($"The item, {key} was found at index {mid} of the array");
        } while (min <= max);

（我正在使用的数组已排序）我只是得到一个空白的控制台，它似乎从未找到结果。我该如何解决？

谢谢

更新：我已经从txt文件创建了float []，如下所示：

float[] floats = (File.ReadAllLines(@"floats.txt")).Where(s => s != String.Empty).Select(s => float.Parse(s)).ToArray();

Here's the contents of floats.txt (link to pastebin)

以下是用于测试算法是否有效的行：

Search(floats, -2.4439f);

（此外，在尝试搜索数组之前，我先对其进行了排序）

Answer 1

使用您提供的输入文件，此代码实际上对我有用。我的猜测是您不是先对数组进行排序：

    static void Main(string[] args)
    {
        // Read in floats from input file
        var lines = File.ReadAllLines(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "input.txt"));
        var floats = new List<float>();
        foreach (var l in lines)
        {
            if (float.TryParse(l, out var result))
            {
                floats.Add(result);
            }
        }

        var array = floats.OrderBy(f => f).ToArray();
        float key = -2.4439f;

        Search(array, key);
    }

    public static void Search(float[] array, float key)
    {
        int min = 0;
        int max = array.Length - 1;
        int mid = 0;

        do
        {
            mid = (min + max) / 2;

            if (key > array[mid])
            {
                min = mid + 1;
            }

            if (key < array[mid])
            {
                max = mid - 1;
            }

            Console.WriteLine($"Checking {array[mid]}");
            if (key == array[mid])
            {
                Console.WriteLine($"The item, {key} was found at index {mid} of the array");
                break;
            }
        } while (min <= max);
    }

这是输出：

The item, -2.4439 was found at index 146 of the array

Answer 2

二进制搜索是递归函数的理想选择。也许您可以尝试这样的事情：

public static void Search(float[] array, float key, int? min = null, int? max = null)
    {
        if (!min.HasValue)
        {
            min = 0;
        }
        if (!max.HasValue)
        {
            max = array.Length - 1;
        }

        Console.WriteLine(string.Format("Searching from {0} to {1}", min.Value, max.Value));

        if (min.Value >= max.Value)
        {
            if (array[min.Value] == key)
            {
                Console.WriteLine(string.Format("The item, {0} was found at index {1} of the array", key, min.Value));
            }
        }
        else
        {
            int mid = (max.Value - min.Value) / 2;
            if (mid < 1)
            {
                mid = 1;
            }
            Search(array, key, min, min.Value + mid - 1);
            Search(array, key, min.Value + mid, max);
        }
    }

如何修复C＃二进制搜索算法？

2 个答案: