Determining loop invariant for a recursive function

Asked May 14 '18 at 20:59

Active May 14 '18 at 23:02

Viewed 383 times

Assume you have a function that returns the difference in length between two arrays, however, it's not using the conventional methods to find length but rather a recursive function.
Can you help me find a loop invariant? I understand the loop invariant is something that must be true before the condition and after the condition. However, I am not really able to understand it. Here's the code:

function func (int arr1_length, int arr2_length) {
   if (arr1_length == 0 && arr2_length == 0) return 0;
   if (arr1_length == 0) return arr2_length;
   if (arr2_length == 0) return arr1_length;
   return func (arr1_length-1, arr2_length-1);
}

The first call is func(arr1.length, arr2.length);

edited May 14 '18 at 23:02

asked May 14 '18 at 20:59

bobaxs31

Small correction: this function is using recursion, not a while loop. – Devin Fields May 14 '18 at 21:06
You're correct, let me update it – bobaxs31 May 14 '18 at 22:59
1

both arguments should be >0 – c0der May 15 '18 at 03:24
1

Deleted my old comment cause I misspoke; both arguments must be > -1, since a starting value of 0 is perfectly fine. – Devin Fields May 15 '18 at 17:16

Determining loop invariant for a recursive function

0 Answers0