Complicated is bad, Simple is good

Challenge Accepted

//Given a list of numbers and a target number X, find the pairs of numbers in the list that add to yield X

//FIRST ATTEMPT: "THE LOOP"

public class Pair
 {
    int First{get;set;}
    int Second{get;set;}

    public Equals(Pair x, Pair y)
    {
        if(x.First == y.First && x.Second == y.Second || x.Second == y.Second && x.Second == y.First) return true;
        else {return false;}
    }
 }
 
 public class Calculate
 {
 
     public List<Pair> FindPairs(List<int> list, int target)
     {

         List<Pair> found = new List<Pair>();
         
         for(int i=0;i<list.Count;i++)
         {
             int current = list[i];
             for(int j=i+1;j<list.Count;j++)
             {
                 if(list[j] == list[i] - target)
                 {
                    Pair newItem = new Pair(){ First = current, Second = list[j] };
                    bool exists = false;
                    foreach(var item in found)
                    {

                        if(item.Equals(newItem))
                        {
                        exists = true;
                        }
                        }
                        if(!exists)
                        {
                            found.Add(newItem);
                        }
                    }
                 }
             }
         }
         
         return found;
     }
 }

//SECOND ATTEMPT: LOOK IN THE DICTIONARY AND TAKE THE HINT
//Inspired by: http://www.kirupa.com/forum/showthread.php?237560-Find-Two-Numbers-in-an-Array-that-Sum-to-a-Particular-Value

public class Pair
{
    int First{get;set;}
    int Second{get;set;}

    public Equals(Pair x, Pair y)
    {
    if(x.First == y.First && x.Second == y.Second || x.Second == y.Second && x.Second == y.First) return true;
    else {return false;}
    }
}

public class Calculate
{

    public List<Pair> FindPairs(List<int> list, int target)
    {
        List<Pair> found = new List<Pair>();
        Dictionary<int,int> find = new Dictionary<in,int>();

        for(int i=0;i<list.Count;i++)
        {
            if(find.Key(list[i])
            {
                Pair newItem = new Pair(){ 
                    First = list[i], 
                    Second = find.Value(list[i]) 
                };
                bool exists = false;
                foreach(item in found)
                {
                    if(item.Equals(newItem))
                    {
                        exists = true;
                    }
                }
                
                if(!exists)
                {
                    found.Add(newItem);
                }
            }
            else
            {
                find.Add(target - list[i], list[i]);
            }
        }
        
        return found;
    }
}