Devise an algorithm to find the number of 'pairs' in an input string. A 'pair' for this question can be defined as a situation in which two instances of the same character are separated by a single other character.

ex. "ZaZ" has one pair made of Z's

ex 2. "ZaZa" has 2 pairs
Solution is O(n).
An O(n) solution involves iterating through the string and comparing the current character with another one character away. The only trick in this question is to pay attention to details: "separated by a single other character". This means we will also need to compare the first or third character to the middle character and ensure they are different. Also be sure to iterate only through 'length - 2' to avoid out of bounds exceptions.