Question
Given a list of integers, scan it from left to right and return the first value you encounter for the second time — in other words, the value whose second occurrence has the smallest index. If no value ever repeats, return -1. For example, in [2, 5, 3, 5, 2] the value 5 completes a repeat at index 3, before 2 does at index 4, so the answer is 5. Aim for a single pass.
first_repeated(nums: list[int]) → int[[2,5,3,5,2]]out5State your approach and its time/space complexity out loud before you optimize. Handle the edge cases (empty input, duplicates, overflow), and say why you chose this over the brute force. Green tests are the floor, not the grade.
Vibe coding: describe the solution in plain language (or narrate it) and the coach grades your approach. Generating runnable code from your description is coming next.