用C＃在int数组中找到min值

Question

如何使用c＃

在int数组中找到min值

Answer 1

使用LINQ：

int min = theArray.Min();

请注意，如果没有任何元素，则会出错;首先检查.Length（或者选择项目int?，但这会增加开销）。

如果您没有可用的LINQ，那么可能：

public static int Min(int[] arr) {
    switch (arr.Length) {
        case 0: throw new InvalidOperationException();
        case 1: return arr[0];
        case 2: return Math.Min(arr[0], arr[1]);
        default:
            int min = arr[0];
            for (int i = 1; i < arr.Length; i++) {
                if (arr[i] < min) min = arr[i];
            }
            return min;
    }
}

Answer 2

我写下来比较我对@Marc Gravell说的话，我说的方式在我的电脑上有点快，而linq是最慢的方式，如果你改变了函数的位置（在代码中），你会使用if

版本时，总能获得更好的性能

    static void Main(string[] args)
    {
        Dictionary<string, List<long>> dic = new Dictionary<string, List<long>>();

        dic["First"] = new List<long>();
        dic["Second"] = new List<long>();
        dic["Third"] = new List<long>();


        for (int i = 0; i < 500; i++)
        {
            int[] array = GetRandomArray();
            Stopwatch stopWacth = new Stopwatch();
            stopWacth.Restart();
            int n1 = FindMin(array);
            stopWacth.Stop();
            long firstTicks = stopWacth.ElapsedTicks;
            dic["First"].Add(firstTicks);

            stopWacth.Restart();
            int n2 = AnotherFindMin(array);
            stopWacth.Stop();
            long secondTick = stopWacth.ElapsedTicks;
            dic["Second"].Add(secondTick);

            stopWacth.Restart();
            int n3 = array.Min();
            stopWacth.Stop();
            long thirdTick = stopWacth.ElapsedTicks;
            dic["Third"].Add(thirdTick);

            Console.WriteLine("first tick : {0}, second tick {1}, third tick {2} ", firstTicks, secondTick, thirdTick);
        }

        Console.WriteLine("first tick : {0}, second tick {1}, third tick {2} ", dic["First"].Average(), dic["Second"].Average(), dic["Third"].Average());

        Console.ReadLine();
    }


    public static int[] GetRandomArray()
    {
        int[] retVal = new int[1000000];
        Random r = new Random();
        for (int i = 0; i < 1000000; i++)
        {
            retVal[i] = r.Next(1000000000);
        }
        return retVal;
    }

    public static int FindMin(int[] arr)
    {
        switch (arr.Length)
        {
            case 0: throw new InvalidOperationException();
            case 1: return arr[0];
            case 2: return Math.Min(arr[0], arr[1]);
            default:
                int min = arr[0];
                for (int i = 1; i < arr.Length; i++)
                {
                    if (arr[i] < min) min = arr[i];
                }
                return min;
        }
    }

    public static int AnotherFindMin(int[] arr)
    {
        if (arr.Length > 0)
        {
            int min = arr[0];
            for (int i = 1; i < arr.Length; i++)
            {
                if (arr[i] < min) min = arr[i];
            }
            return min;
        }
        else
        {
            throw new InvalidOperationException();
        }
    }
}
// revised test by Marc (see comments discussion)
static class Test {
    static void Main(string[] args)
    {
        Dictionary<string, List<long>> dic = new Dictionary<string, List<long>>();

        dic["First"] = new List<long>();
        dic["Second"] = new List<long>();
        dic["Third"] = new List<long>();

        const int OUTER_LOOP = 500, INNER_LOOP = 500000;
        for (int arrSize = 1; arrSize <= 3; arrSize++)
        {
            for (int i = 0; i < OUTER_LOOP; i++)
            {
                int[] array = GetRandomArray(arrSize);
                Stopwatch stopWacth = Stopwatch.StartNew();
                for (int j = 0; j < INNER_LOOP; j++)
                {
                    int n1 = FindMin(array);
                }
                stopWacth.Stop();
                long firstTicks = stopWacth.ElapsedTicks;
                dic["First"].Add(firstTicks);

                stopWacth = Stopwatch.StartNew();
                for (int j = 0; j < INNER_LOOP; j++)
                {
                    int n2 = AnotherFindMin(array);
                }
                stopWacth.Stop();
                long secondTick = stopWacth.ElapsedTicks;
                dic["Second"].Add(secondTick);

                stopWacth = Stopwatch.StartNew();
                for (int j = 0; j < INNER_LOOP; j++)
                {
                    int n3 = array.Min();
                }
                stopWacth.Stop();
                long thirdTick = stopWacth.ElapsedTicks;
                dic["Third"].Add(thirdTick);

                //Console.WriteLine("{3}: switch : {0}, 0-check {1}, Enumerable.Min {2} ", firstTicks, secondTick, thirdTick, arrSize);
            }

            Console.WriteLine("{3}: switch : {0}, 0-check {1}, Enumerable.Min {2} ", dic["First"].Average(), dic["Second"].Average(), dic["Third"].Average(), arrSize);
        }
        Console.WriteLine("Done");
        Console.ReadLine();
    }


    public static int[] GetRandomArray(int size)
    {
        int[] retVal = new int[size];
        Random r = new Random();
        for (int i = 0; i < retVal.Length; i++)
        {
            retVal[i] = r.Next(1000000000);
        }
        return retVal;
    }

    public static int FindMin(int[] arr)
    {
        switch (arr.Length)
        {
            case 0: throw new InvalidOperationException();
            case 1: return arr[0];
            case 2: return arr[0] < arr[1] ? arr[0] : arr[1];
            default:
                int min = arr[0];
                for (int i = 1; i < arr.Length; i++)
                {
                    if (arr[i] < min) min = arr[i];
                }
                return min;
        }
    }

    public static int AnotherFindMin(int[] arr)
    {
        if (arr.Length > 0)
        {
            int min = arr[0];
            for (int i = 1; i < arr.Length; i++)
            {
                if (arr[i] < min) min = arr[i];
            }
            return min;
        }
        else
        {
            throw new InvalidOperationException();
        }
    }
}