Given an array a that contains only numbers in the range from 1 to a.length, find the first duplicate number for which the second occurrence has the minimal index. In other words, if there are more than 1 duplicated numbers, return the number for which the second occurrence has a smaller index than the second occurrence of the other number does. If there are no such elements, return -1.
For a = [2, 3, 3, 1, 5, 2]
, the output should be
firstDuplicate(a) = 3
.
There are 2 duplicates: numbers 2 and 3. The second occurrence of 3 has a smaller index than than second occurrence of 2 does, so the answer is 3.
For a = [2, 4, 3, 5, 1]
, the output should be
firstDuplicate(a) = -1
.
Here is my solution 11 Run tests approved