查找列表中的元素,这些元素加起来等于目标数 [英] Find elements in a list that, together add up to a target number
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问题描述
假设我有一个列表:
List<int> _arr = new List<int> {1, 3, 4};
目标4
我想使用给定列表中的linq返回{1, 3}
作为1 + 3 = 4
和{4}
作为4 = 4
.
I want to return {1, 3}
as 1 + 3 = 4
and {4}
as 4 = 4
using linq from the given list.
我该怎么做?
推荐答案
一旦有了一种获取枚举器/列表的所有子集的方法,这很容易
(在这里找到:答案:最优雅的方式来获取C#中数组的所有子集)
It's easy once we have a method to get all subsets of an enumerator/list
(found here: Answer: Most Elegant Way to Get All Subsets of an Array in C#)
using System;
using System.Collections.Generic;
using System.Linq;
public static class Program
{
static void Main(string[] args)
{
var test = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
var target = 6;
var matches = from subset in test.SubSetsOf()
where subset.Sum() == target
select subset;
Console.WriteLine("Numbers: {0}", test.Select(i => i.ToString()).Aggregate((a, n) => a + ", " + n));
Console.WriteLine("Target: {0}", target);
foreach (var match in matches)
{
Console.WriteLine(match.Select(m => m.ToString()).Aggregate((a, n) => a + " + " + n) + " = " + target.ToString());
}
Console.ReadKey();
}
public static IEnumerable<IEnumerable<T>> SubSetsOf<T>(this IEnumerable<T> source)
{
// Deal with the case of an empty source (simply return an enumerable containing a single, empty enumerable)
if (!source.Any())
return Enumerable.Repeat(Enumerable.Empty<T>(), 1);
// Grab the first element off of the list
var element = source.Take(1);
// Recurse, to get all subsets of the source, ignoring the first item
var haveNots = SubSetsOf(source.Skip(1));
// Get all those subsets and add the element we removed to them
var haves = haveNots.Select(set => element.Concat(set));
// Finally combine the subsets that didn't include the first item, with those that did.
return haves.Concat(haveNots);
}
}
输出:
Numbers: 1, 2, 3, 4, 5, 6, 7, 8, 9
Target: 6
1 + 2 + 3 = 6
1 + 5 = 6
2 + 4 = 6
6 = 6
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