Leetcode preparation

Easy problems: 64.2% Completed
Medium problems: 49.3% Completed
Hard problems: 35.3% Completed

I've been doing the LeetCode interview assesments for Facebook and also doing some codeforces problems.

Technical phone screen (1 hour)

I was asked two coding questions (no android questions):

• Given an array of n integers, return an array of n integers where at each position 0 <= i < n contains the multiplication of all the integers in the original array, except the one at the position i. This is the problem in Leetcode https://leetcode.com/problems/product-of-array-except-self/
• Given an array of n integers, return using a normal distribution any index i that belongs to the highest integer in the array. It is really similar to this Leetcode problem https://leetcode.com/problems/random-pick-index/, just that your target is the highest number in the array.

Results: Resolved both questions in less than 40 minutes and passed to virtual onsite interview

Virtual onsite interview (4 rounds)

I did pass to the next step which as you all may know, is 4 rounds of interviews. In my case they were organized this way:
2 Coding Interview, 1 Design Interview, 1 Behavioral Interview.

1st Coding round

• Given a string s return if it is either a palindrome or a palindrome + 1 extra character. Similar leetcode question: https://leetcode.com/problems/valid-palindrome-ii/
• Given an array of n integers, return its next permutation. Similar leetcode question https://leetcode.com/problems/next-permutation/

Results: Resolved both questions in less than 40 minutes. I did O(n^2) for the first one and O(nlogn) for the second one

2nd Coding round

• Given a string with parenthesis, return how many parenthesis do we need to add to make it valid. Similar leetcode question https://leetcode.com/problems/minimum-add-to-make-parentheses-valid/
• Given a string, simulate the 'deletion' of a Candy Crash in 1D. The result string should not contain two same character next to each other. Similar leetcode question https://leetcode.com/problems/remove-all-adjacent-duplicates-in-string/

Reuslts: Resolved both questions in less than 40 minutes. I did O(n) for the first one and O(n^2) for the second one

Design round

Design the Instagram home screen.
After asking some questions I got the following list of requirements:

• Authentication with Facebook
• List of posts (need to handle a large amount of posts)
• Each post has only one image
• I can like / dislike each post
• Each post shows the user's profile photo on top of them
• The app should work in offline mode (for example if I am in the airplane I should see what I already loaded)

Results: I was scaried about this round, but at the end I think I did this really good. I was able to come up with a final design talking about offline mode, about RecyclerView optimizations, how to deal with cache for images (what does libraries like Glide / Piccaso do under the hood), WorkManager, batching requests and pagination.

Behavioral round

This was mainly a conversation between the interview and I. I was asked to give examples about some specific situations in my past experiences like: 'tal about when you got an ambiguous requirement' or 'talk about when you had to work with someone you dislike'.

At the end there was a coding question: Given an array of chracters, return its number representation (ignore characters that are no numbers). Similar Leetcode question: https://leetcode.com/problems/string-to-integer-atoi/

Results: I think I did it well during the first part, I talked about my past experience and how did I face the situations I was asked to answer. I did resolve the question pretty quickly too, I think I missed some edge cases like empty spaces at the beginning, but at least the interview was apparently ok with my solution. I did O(n) solution.