Given an array a, find the greatest number in a that is a product of two elements in a. If there are no two elements in a that can be multiplied to produce another element contained in a, return -1.

I am trying to get this to run as fast as possible. I assume there is some math algorithm or formula to do this that I am unaware of. This is the way I know how to find this answer. However, I assume this would take a long time if the length of the array was huge. Is there a faster way to do this? I have provided the test.

using System;
using System.Linq;

namespace Exercise
{
    public static class Program
    {
        public static int maxPairProduct(int[] a)
        {
            int x = -1;

            for (int i = 0; i < a.Length; ++i)
            {
                for (int j = i + 1; j < a.Length; ++j)
                {
                    int temp = a[i] * a[j];
                    if (a.Contains(temp) && temp > x)
                    {
                        x = temp;
                    }
                }
            }
            return x;
        }
    }
}

using NUnit.Framework;

namespace Exercise
{
    public class SuccessTests
    {
        [Test]
        public static void TestOne() => Assert.That(Program.maxPairProduct(new int[] { 10, 3, 5, 30, 35 }), Is.EqualTo(30));
        public static void TestTwo() => Assert.That(Program.maxPairProduct(new int[] { 2, 5, 7, 8 }), Is.EqualTo(-1));

    }
}
```

Given an array a, find the greatest number in a that is a product of two elements in a. If there are no two elements in a that can be multiplied to produce another element contained in a, return -1.

I am trying to get this to run as fast as possible. I assume there is some math algorithm or formula to do this that I am unaware of. This is the way I know how to find this answer. However, I assume this would take a long time if the length of the array was huge. Is there a faster way to do this? I have provided the test.

using System;
using System.Linq;

namespace Exercise
{
    public static class Program
    {
        public static int maxPairProduct(int[] a)
        {
            int x = -1;

            for (int i = 0; i < a.Length; ++i)
            {
                for (int j = i + 1; j < a.Length; ++j)
                {
                    int temp = a[i] * a[j];
                    if (a.Contains(temp) && temp > x)
                    {
                        x = temp;
                    }
                }
            }
            return x;
        }
    }
}

using NUnit.Framework;

namespace Exercise
{
    public class SuccessTests
    {
        [Test]
        public static void TestOne() => Assert.That(Program.maxPairProduct(new int[] { 10, 3, 5, 30, 35 }), Is.EqualTo(30));
        public static void TestTwo() => Assert.That(Program.maxPairProduct(new int[] { 2, 5, 7, 8 }), Is.EqualTo(-1));

    }
}

Given an array a, find the greatest number in a that is a product of two elements in a. If there are no two elements in a that can be multiplied to produce another element contained in a, return -1.

I am trying to get this to run as fast as possible. I assume there is some math algorithm or formula to do this that I am unaware of. This is the way I know how to find this answer. However, I assume this would take a long time if the length of the array was huge. Is there a faster way to do this? I have provided the test.

using System;
using System.Linq;

namespace Exercise
{
    public static class Program
    {
        public static int maxPairProduct(int[] a)
        {
            int x = -1;

            for (int i = 0; i < a.Length; ++i)
            {
                for (int j = i + 1; j < a.Length; ++j)
                {
                    int temp = a[i] * a[j];
                    if (a.Contains(temp) && temp > x)
                    {
                        x = temp;
                    }
                }
            }
            return x;
        }
    }
}

using NUnit.Framework;

namespace Exercise
{
    public class SuccessTests
    {
        [Test]
        public static void TestOne() => Assert.That(Program.maxPairProduct(new int[] { 10, 3, 5, 30, 35 }), Is.EqualTo(30));
        public static void TestTwo() => Assert.That(Program.maxPairProduct(new int[] { 2, 5, 7, 8 }), Is.EqualTo(-1));

    }
}

Given an array a, find the greatest number in a that is a product of two elements in a. If there are no two elements in a that can be multiplied to produce another element contained in a, return -1.

I am trying to get this to run as fast as possible. I assume there is some math algorithm or formula to do this that I am unaware of. This is the way I know how to find this answer. However, I assume this would take a long time if the length of the array was huge. Is there a faster way to do this? I have provided the test.

using System;
using System.Linq;

namespace Exercise
{
    public static class Program
    {
        public static int maxPairProduct(int[] a)
        {
            int x = -1;

            for (int i = 0; i < a.Length; ++i)
            {
                for (int j = i + 1; j < a.Length; ++j)
                {
                    int temp = a[i] * a[j];
                    if (a.Contains(temp) && temp > x)
                    {
                        x = temp;
                    }
                }
            }
            return x;
        }
    }
}

using NUnit.Framework;

namespace Exercise
{
    public class SuccessTests
    {
        [Test]
        public static void TestOne() => Assert.That(Program.maxPairProduct(new int[] { 10, 3, 5, 30, 35 }), Is.EqualTo(30));
        public static void TestTwo() => Assert.That(Program.maxPairProduct(new int[] { 2, 5, 7, 8 }), Is.EqualTo(-1));

    }
}
```