444. Find First Duplicate Index Sum

Given an array of integers, find the sum of the indices of the first occurrence of every unique number. If a number appears more than once in the array, its first occurrence index should still be included in the sum. If the array is empty, return 0.

Example:
Input: [1,2,3,1,4,2]
Output: 7

Run this challenge interactively in Python or JavaScript when the app loads.