C#-用LinQ提取符合条件的数据

Question

数组{1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19}
要找出那些数相加等于20，用 LinQ如何实现

Answer 1

var results = from a in array
from b in array
where a + b == 20 && a < b //无重复，有重复用<=。如果求有序对的话不加
select new{First = a, Second = b};

这才叫LINQ
编译出来大概变成这样

var results = array.SelectMany(x=>array.Where(y=>x+y==20 && x < y).Select(y=>new{First=x, Second=y}));

三个、四个的情况你还问么……
顺便可变数量的情况

IEnumerable<IEnumerable<int>> GetAll(int[] array, int num, int sum, int limit)
{
if(num == 1)
return array.Where(x=>x==sum && x > limit).Select(x=>new int[]{x});
else
return from a in array
from b in GetAll(array, num - 1, sum - a, a)
select new int[]{a}.Concat(b);
}

效率嘛当然不算太高了

Answer 2

static void Main(string[] args)
{
int[] Temp = new int[19]{ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 };
List<string> list=new List<string>();
Temp.ToList().ForEach(f => Temp.Where(w => f + w == 20).Where(w=>{list.Add(w.ToString()+"|"+f.ToString());return true;}).Select(s=>s).FirstOrDefault());
}

上面代码我就不解释了，基本上一眼能看懂的，能满足你的要求