C# 随机算法直到满足条件

Question

我有以下场景:

1. 从一定范围内生成n个随机数
2. 对所有数字求和
3. 检查sum == x(x是用户设置的数字)
4. if sum != x then keep running the loop
5. 如果 sum == x，则显示总和为 x 的随机数列表

根据这个逻辑，我是可以这样做的，但是需要很长时间才能达到结果，有没有更好的/方法来解决这个问题？

    static void Main(string[] args)
    {
        Console.WriteLine("starting...");
        List<int> checkList = generate(5);
        while(!checkSum(checkList, 100))
        {
            checkList = generate(5)
        }
        Console.WriteLine("done!");
    }


    private static bool checkSum(List<int> n, int sum)
    {
        if(n.Sum() == sum)
        {
            return true;
        }
        else
        {
            return false;
        }
    }


    public static List<int> generate(int n)
    {
        Random rng = new Random();
        List<int> list = new List<int>();
        for (int i = 0; i < 5; i++)
        {
            //int ran = some random number
            list.Add(ran);
        }

        return list;
    }

编辑

我的场景是获取总和为 100 的随机整数的 n 组合。组合的数量取自用户的输入。因此程序将给出 n 种可能的组合，总和为 100。

可能的组合:

• 25+37+9+20+9 = 100
• 46+21+13+8+12 = 100

Answer 1

如果您有一个固定的总和和固定数量的元素，请将问题视为分区。例如:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace PartitionAndAllocateTEst
{
    class Program
    {
        static void Main(string[] args)
        {
            var rand = new Random();
            int desiredTotal = 100;
            int partitions = 5;

            for (int i = 0; i < 10; i++)
            {
                List<int> result = GetRandomCollection(rand, desiredTotal, partitions);
                Console.WriteLine(string.Join(", ", result.Select(r => r.ToString()).ToArray()));
            }
        }

        private static List<int> GetRandomCollection(Random rand, int desiredTotal, int partitions)
        {
            // calculate the weights
            var weights = new List<double>();
            for (int i = 0; i < partitions; i++)
            {
                weights.Add(rand.NextDouble());
            }
            var totalWeight = weights.Sum();

            // allocate the integer total by weight
            // http://softwareengineering.stackexchange.com/questions/340393/allocating-an-integer-sum-proportionally-to-a-set-of-reals/340394#340394
            var result = new List<int>();
            double allocatedWeight = 0;
            int allocatedCount = 0;
            foreach (var weight in weights)
            {
                var newAllocatedWeight = allocatedWeight + weight;
                var newAllocatedCount = (int)(desiredTotal * (newAllocatedWeight / totalWeight));
                var thisAllocatedCount = newAllocatedCount - allocatedCount;
                allocatedCount = newAllocatedCount;
                allocatedWeight = newAllocatedWeight;

                result.Add(thisAllocatedCount);
            }

            return result;
        }
    }
}

示例输出:

30, 6, 19, 15, 30
36, 8, 22, 10, 24
2, 25, 32, 21, 20
22, 7, 30, 12, 29
36, 21, 22, 0, 21
24, 24, 2, 29, 21
18, 13, 10, 39, 20
11, 19, 20, 27, 23
24, 19, 7, 25, 25
24, 14, 27, 18, 17