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firstDuplicate.ts
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README.md

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Algorithm Challenge Available At CodeFights

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.

Example

  • For a = [2, 1, 3, 5, 3, 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 the second occurrence of 2 does, so the answer is 3.

  • For a = [2, 4, 3, 5, 1], the output should be firstDuplicate(a) = -1.

Hints

  • hasOwnProperty()

Input/Output

  • [execution time limit] 5 seconds (ts)

  • [input] array.integer a

A string containing at least one digit.

Guaranteed constraints:

1 ≤ a.length ≤ 105, 1 ≤ a[i] ≤ a.length.

  • [output] integer The element in a that occurs in the array more than once and has the minimal index for its second occurrence. If there are no such elements, return -1.