learn-co-curriculum / find-first-duplicate

algorithms and data structures

Day 2: Find First Duplicate

Learning Goals

• Practice algorithmic problem solving

Instructions

Given an Array, find the first duplicate value that occurs. If there are no duplicates, return -1.

Input: [2, 1, 3, 3, 2]
Output: 3

Input: [1, 2, 3, 4]
Output: -1

Use the language of your choosing. We've included starter files for some languages where you can pseudocode, explain your solution and code.

Before you start coding

1. Rewrite the problem in your own words
2. Validate that you understand the problem
3. Write your own test cases
4. Pseudocode
5. Code!

And remember, don't run our tests until you've passed your own!

How to run your own tests

Ruby

1. cd into the ruby folder
2. ruby <filename>.rb

JavaScript

1. cd into the javascript folder
2. node <filename>.js

How to run our tests

Ruby

1. cd into the ruby folder
2. bundle install
3. rspec

JavaScript

1. cd into the javascript folder
2. npm i
3. npm test

find-first-duplicate's Issues

Add extra test case?

Canvas Link

https://learning.flatironschool.com/courses/4997/assignments/165451?module_item_id=357010

Concern

Could we clarify, in both the README and the test cases, that the duplicates don't have to be next to each other?

For example, I was thinking, After this test,

expect(findFirstDuplicate([1, 2, 3, 3, 2, 1])).toBe(3);

We could add another

expect(findFirstDuplicate([1, 2, 3, 4, 2, 3, 1])).toBe(2);

This test case communicates that 1) duplicates don't have to be next to each other, and 2) when there are multiple duplicates, such as 2s and 3s, the first one is the desired result (2, in this case).

This is all, of course, assuming that I have read and interpreted this assignment correctly, of course.

Additional Context

No response

Suggested Changes

No response

Spec allows for solutions that don't check for arrays without duplicates

For example, this should return -1:

find_first_duplicate([1, 2, 3])