我使用了这个问题Find out which combinations of numbers in a set add up to a given total,该问题使用一个C#示例来尝试查找所有可能的数字组合,这些数字加起来就等于一个给定的数字。
我使用了提供的代码并试图理解它,但我想我确实知道,但是我无法弄清楚为什么会发生此错误。
这是设置:
public class Program
{
public static void Main(string[] args)
{
// subtotal list
List<double> totals = new List<double>(new double[] { 17.5, 14.3, 10.9, 7.8, 6.3, 3.8, 3.2, 2.7, 1.8, 1.0 });
List<double> totals2 = new List<double>(new double[] { 17.5, 14.3, 7.8, 6.3, 3.2, 1.8});
// get matches
List<double[]> results = Knapsack.MatchTotal(50.9, totals2);
// print results`
foreach (var result in results)
{
Console.WriteLine(string.Join(",", result));
}
Console.WriteLine("Done.");
Console.ReadKey();
}
}
和示例中的大部分代码相同。
public class Knapsack
{
internal static List<double[]> MatchTotal(double theTotal, List<double> subTotals)
{
List<double[]> results = new List<double[]>();
while (subTotals.Contains(theTotal))
{
results.Add(new double[1] { theTotal });
subTotals.Remove(theTotal);
}
// if no subtotals were passed
// or all matched the Total
// return
if (subTotals.Count == 0)
return results;
subTotals.Sort();
double mostNegativeNumber = subTotals[0];
if (mostNegativeNumber > 0)
mostNegativeNumber = 0;
// if there aren't any negative values
// we can remove any values bigger than the total
if (mostNegativeNumber == 0)
subTotals.RemoveAll(d => d > theTotal);
// if there aren't any negative values
// and sum is less than the total no need to look further
if (mostNegativeNumber == 0 && subTotals.Sum() < theTotal)
return results;
// get the combinations for the remaining subTotals
// skip 1 since we already removed subTotals that match
for (int choose = 2; choose <= subTotals.Count; choose++)
{
// get combinations for each length
IEnumerable<IEnumerable<double>> combos = Combination.Combinations(subTotals.AsEnumerable(), choose);
// add combinations where the sum mathces the total to the result list
results.AddRange(from combo in combos
where combo.Sum() == theTotal
select combo.ToArray());
}
return results;
}
}
public static class Combination
{
public static IEnumerable<IEnumerable<T>> Combinations<T>(this IEnumerable<T> elements, int choose)
{
return choose == 0 ? // if choose = 0
new[] { new T[0] } : // return empty Type array
elements.SelectMany((element, i) => // else recursively iterate over array to create combinations
elements.Skip(i + 1).Combinations(choose - 1).Select(combo => (new[] { element }).Concat(combo)));
}
}
我提供了totals
中的一组数字,用于尝试计算总数。
我输入了50.9作为总计,没有返回任何结果。
第二组数字totals2
是一组数字之和,总计为50.9,它们是totals
的子集。这也无法返回50.9的结果
由于某种原因,代码无法在主集合或子集中找到50.9(子集本身为50.9)。
我不知道为什么这样做,有人可以告诉我吗?