title: Is there any other way to extract pairs of elements from the array?
body: <p>I'am thinking about extract pairs of elements from ArrayList</p>
  
  <p>for example, ArrayList's value is [1, 2, 3, 4, 5, 6, 7, 8, 9 . . . 100] and I should make pairs of it. </p>
  
  <p>Simple way is to make sequentially (1, 2) (1, 3) (1, 4) ..(1, 100) (2, 3) (2, 4) (2, 5) . . ..(99, 100)</p>
  
  <p>However, if there are 50000 elements in the array, It takes so long time.</p>
  
  <p>I wonder if there's any special way.</p>