In Santa's toy factory at the North Pole, each toy has a unique identification number.
However, due to a glitch in the toy-making machine, some numbers have been assigned to more than one toy.
Your task is to find the first identification number that has been repeated, where the second occurrence has the smallest index!
In simpler terms, if there are multiple repeated numbers, return the number whose second occurrence appears first in the list. If no numbers are repeated, return -1.
const giftIds = [2, 1, 3, 5, 3, 2];
const firstRepeatedId = findFirstRepeated(giftIds);
console.log(firstRepeatedId); // 3
// Although both 2 and 3 are repeated,
// 3 appears first for the second time
const giftIds2 = [1, 2, 3, 4];
const firstRepeatedId2 = findFirstRepeated(giftIds2);
console.log(firstRepeatedId2); // -1
// It's -1 as no number is repeated
const giftIds3 = [5, 1, 5, 1];
const firstRepeatedId3 = findFirstRepeated(giftIds3);
console.log(firstRepeatedId3); // 5Be cautious! The elves say that this is a Google technical test.