README.md

Challenge #1: 🎁 First gift repeated!

In the North Pole toy factory, each toy has a unique identification number.

However, due to an error in the toy machine, some numbers have been assigned to more than one toy.

Find the first identification number that has been repeated, where the second occurrence has the smallest index!

In other words, if there is more than one repeated number, you should return the number whose second occurrence appears first in the list. If there are no repeated numbers, return -1.

const giftIds = [2, 1, 3, 5, 3, 2];
const firstRepeatedId = findFirstRepeated(giftIds);
console.log(firstRepeatedId); // 3
// Even though 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 is -1 since no number is repeated.

const giftIds3 = [5, 1, 5, 1];
const firstRepeatedId3 = findFirstRepeated(giftIds3);
console.log(firstRepeatedId3); // 5

Note

The elves say this is a Google technical test.

Solution

JavaScript

330 points

function findFirstRepeated(gifts) {
  const repeated = gifts.filter((gift, i) => gifts.indexOf(gift) !== i);
  return repeated.length > 0 ? repeated[0] : -1;
}

TypeScript

330 points

function findFirstRepeated(gifts: number[]): number {
  const repeated = gifts.filter((gift, i) => gifts.indexOf(gift) !== i);
  return repeated.length > 0 ? repeated[0] : -1;
}