寻找一个目标数字是通过LINQ得到的数组中的两个数字的总和，并获得和索引

Question

您好，我是Linq的新手，我发现这个线程可以解释我需要的90％ https://stackoverflow.com/questions/2331882?tab=newest#tab-top，感谢“pdr”

，但我需要的是让指数过，这是我修改我得到的第一个数字的索引，但我不知道如何获得的第二个数字

  int[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9 }; 
     var result = from item in numbers.Select((n1, idx) => 
      new { n1,idx, shortList = numbers.Take(idx) }) 
        from n2 in item.shortList 
        where item.n1 + n2 == 7 
        select new { nx1 = item.n1,index1=item.idx, nx2=n2 }; 

Answer 1

SelectMany is你需要什么...

int[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9 }; 
int target = 7; 

var query = numbers 
       .SelectMany((num1,j) => numbers.Select((num2,i) => new {n1=num1, n2=num2, i=i, j=j})) 
       .Where(x => x.n1 + x.n2 == target && x.i < x.j); 

foreach (var x in query)   
    Console.WriteLine(x.n1 + " and " + x.n2 + " occur at " + x.i + "," + x.j); 

Answer 2

该指数会给你一对项目，每个项目都包含来自数组及其索引的值。这些对被限制在值的总和等于目标的地方。 Where子句中的& &消除重复项和自我匹配（适用于偶数目标）。

int[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9 }; 

int target = 7; 

var query = from item1 in numbers.Select((number, index) => new { Number = number, Index = index }) 
      from item2 in numbers.Select((number, index) => new { Number = number, Index = index }) 
      where item1.Number + item2.Number == target 
      && item1.Index < item2.Index 
      select new { Item1 = item1, Item2 = item2 }; 

foreach (var itemPair in query) 
{ 
    Console.WriteLine("{0}:{1}\t{2}:{3}", 
     itemPair.Item1.Index, 
     itemPair.Item1.Number, 
     itemPair.Item2.Index, 
     itemPair.Item2.Number); 
} 

Answer 3

如果它绝对超过一个阵列那么你可以这样做：

var result = from index1 in Enumerable.Range(0, numbers.Length) 
      from index2 in Enumerable.Range(index1 + 1, 
              numbers.Length - index - 1) 
      where numbers[index1] + numbers[index2] == targetNumber 
      select new { index1, index2, 
          value1 = numbers[index1], value2 = numbers[index2] }; 

否则，您可以使用Select形式包括指数两次：

var result = from pair1 in numbers.Select((value, index) => new { value, index}) 
      from pair2 in numbers.Skip(pair1.index + 1) 
            .Select((value, index) => 
            new { value, index = index - pair2.index - 1}) 
      where pair1.value + pair2.value == targetNumber 
      select new { index1 = pair1.index, index2 = pair2.index, 
          value1 = pair1.value, value2 = pair2.value }; 

两个这些真的很难看......