title: Two Sorted Arrays, sum of 2 elements equal a certain number
body: <p>I was wondering if I could get some help. I want to find an algorithm that is THETA(n) or linear time for determining whether 2 numbers in a 2 sorted arrays add up to a certain number.</p>
  
  <p>For instance, let's say we have 2 sorted arrays: X and Y</p>
  
  <p>I want to determine if there's an element of X and an element of Y that add up to exactly a certain number, let's say 50.</p>
  
  <p>I have been able to come up with these algorithms in Python so far, but I am pretty sure they are order of THETA(n^2) rather than THETA(n).</p>
  
  <pre><code>def arrayTestOne(X,Y):
      S =[1 for x in X for y in Y if x+y == 50]
  
  def arrayTestTwo(X,Y):
      for x in X:
          for y in Y:
              if x + y == 50:
                  print("1")
  </code></pre>
  
  <p>I'm thinking it's the double for loops that break the linear time, but how else would you iterate through 2 lists? Any thoughts would be appreciated.</p>