1.4.38 #

public static class DoubleTest
{
    private static readonly int MaximumInteger = 1000000;

    /// <summary>
    /// 返回对 n 个随机整数的数组进行一次 ThreeSum 所需的时间。
    /// </summary>
    /// <param name="n">随机数组的长度。</param>
    /// <returns></returns>
    public static double TimeTrial(int n)
    {
        var a = new int[n];
        var random = new Random(DateTime.Now.Millisecond);
        for (var i = 0; i < n; i++)
        {
            a[i] = random.Next(-MaximumInteger, MaximumInteger);
        }
        var timer = new Measurement.Stopwatch();
        ThreeSum.Count(a);
        return timer.ElapsedTime();
    }
}

public static class ThreeSum
{
    /// <summary>
    /// 输出所有和为零的三元组。
    /// </summary>
    /// <param name="a">输入数组。</param>
    public static void PrintAll(int[] a)
    {
        var n = a.Length;
        for (var i = 0; i < n; i++)
        {
            for (var j = 0; j < n; j++)
            {
                for (var k = 0; k < n; k++)
                {
                    if (i < j && j < k)
                    {
                        if ((long)a[i] + a[j] + a[k] == 0)
                        {
                            Console.WriteLine($"{a[i]} + {a[j]} + {a[k]}");
                        }
                    }
                }
            }
        }
    }

    /// <summary>
    /// 计算和为零的三元组的数量。
    /// </summary>
    /// <param name="a">输入数组。</param>
    /// <returns></returns>
    public static int Count(int[] a)
    {
        var n = a.Length;
        var count = 0;
        for (var i = 0; i < n; i++)
        {
            for (var j = 0; j < n; j++)
            {
                for (var k = 0; k < n; k++)
                {
                    if (i < j && j < k)
                    {
                        if ((long)a[i] + a[j] + a[k] == 0)
                        {
                            count++;
                        }
                    }
                }
            }
        }
        return count;
    }
}