What is the most efficient pattern/algorithm to compare two lists and find the delta between those two lists?

Question

We have two lists, let\'s say students and their scores. I want to compare these two lists and find the delta between the new list and the old list, then find the least intrusi

Answer 1

If you're looking for a general, language-agnostic solution, then you're looking for some kind of data synchronization of ordered lists. The basic algorithm would be:

i1 = 0
i2 = 0
while (i1 < list1.size && i2 < list2.size)
{
  if (list1[i1] < list2[i2])
  {
    //list1[i1] is not in list2
    i1++
  }
  else if (list1[i1] > list2[i2])
  {
    //list2[i2] is not in list1
    i2++
  }
  else
  {
    //item is in both lists
    i1++
    i2++
  }
}
if (i1 < list1.size)
   //all remaining list1 items are not in list2
if (i2 < list2.size)
   //all remaining list2 items are not in list1