dailycodingproblem.com

This repo contains my solutions to the tasks from dailycodingproblem.com.

Lessons

1. How to solve a hard programming interview questions
2. How to formulaically solve tree interview questions

My solutions

Number	Title	Difficulty	Questioner	Description
17	longest filepath	Hard	Google	Suppose we represent our file system by a string in the following manner: The string "dir\n\tsubdir1\n\tsubdir2\n\t\tfile.ext" represents: dir subdir1 subdir2 file.ext The directory dir contains an empty sub-directory subdir1 and a sub-directory subdir2 containing a file file.ext. The string "dir\n\tsubdir1\n\t\tfile1.ext\n\t\tsubsubdir1\n\tsubdir2\n\t\tsubsubdir2\n\t\t\tfile2.ext" represents: dir subdir1 file1.ext subsubdir1 subdir2 subsubdir2 file2.ext The directory dir contains two sub-directories subdir1 and subdir2. subdir1 contains a file file1.ext and an empty second-level sub-directory subsubdir1. subdir2 contains a second-level sub-directory subsubdir2 containing a file file2.ext. We are interested in finding the longest (number of characters) absolute path to a file within our file system. For example, in the second example above, the longest absolute path is "dir/subdir2/subsubdir2/file2.ext", and its length is 32 (not including the double quotes). Given a string representing the file system in the above format, return the length of the longest absolute path to a file in the abstracted file system. If there is no file in the system, return 0. Note: The name of a file contains at least a period and an extension. The name of a directory or sub-directory will not contain a period.
16	recent record	Easy	Twitter	You run an e-commerce website and want to record the last N order ids in a log. Implement a data structure to accomplish this, with the following API: record(order_id): adds the order_id to the log get_last(i): gets the ith last element from the log. i is guaranteed to be smaller than or equal to N. You should be as efficient with time and space as possible.
14	monte carlo pi approximation	Medium	Google	The area of a circle is defined as πr^2. Estimate π to 3 decimal places using a Monte Carlo method. Hint: The basic equation of a circle is x^2 + y^2 = r^2.
13	longest substring with k distinct characters	Hard	Amazon	Given an integer k and a string s, find the length of the longest substring that contains at most k distinct characters. For example, given s = "abcba" and k = 2, the longest substring with k distinct characters is "bcb".
12	staircase climbing	Hard	Amazon	There exists a staircase with N steps, and you can climb up either 1 or 2 steps at a time. Given N, write a function that returns the number of unique ways you can climb the staircase. The order of the steps matters. For example, if N is 4, then there are 5 unique ways: - 1, 1, 1, 1 - 2, 1, 1 - 1, 2, 1 - 1, 1, 2 - 2, 2 What if, instead of being able to climb 1 or 2 steps at a time, you could climb any number from a set of positive integers X? For example, if X = {1, 3, 5}, you could climb 1, 3, or 5 steps at a time.
11	autocomplete	Medium	Twitter	Implement an autocomplete system. That is, given a query string s and a set of all possible query strings, return all strings in the set that have s as a prefix. For example, given the query string de and the set of strings [dog, deer, deal], return [deer, deal]. Hint: Try preprocessing the dictionary into a more efficient data structure to speed up queries.
9	largest sum of non adjacent numbers	Hard	Airbnb	Given a list of integers, write a function that returns the largest sum of non-adjacent numbers. Numbers can be 0 or negative. For example, [2, 4, 6, 2, 5] should return 13, since we pick 2, 6, and 5. [5, 1, 1, 5] should return 10, since we pick 5 and 5. Follow-up: Can you do this in O(N) time and constant space?
8	unival tree	Easy	Google	A unival tree (which stands for "universal value") is a tree where all nodes under it have the same value. Given the root to a binary tree, count the number of unival subtrees.
7	number of interpretations	Medium	Facebook	Given the mapping a = 1, b = 2, ... z = 26, and an encoded message, count the number of ways it can be decoded. For example, the message '111' would give 3, since it could be decoded as 'aaa', 'ka', and 'ak'. You can assume that the messages are decodable. For example, '001' is not allowed.
6	xor linked list	Hard	Google	An XOR linked list is a more memory efficient doubly linked list. Instead of each node holding next and prev fields, it holds a field named both, which is an XOR of the next node and the previous node. Implement an XOR linked list; it has an add(element) which adds the element to the end, and a get(index) which returns the node at index. If using a language that has no pointers (such as Python), you can assume you have access to get_pointer and dereference_pointer functions that converts between nodes and memory addresses.
5	cons car cdr	Medium	Jane Street	cons(a, b) constructs a pair, and car(pair) and cdr(pair) returns the first and last element of that pair. For example, car(cons(3, 4)) returns 3, and cdr(cons(3, 4)) returns 4. Given this implementation of cons: def cons(a, b): def pair(f): return f(a, b) return pair Implement car and cdr.
4	lowest positive integer not in array	Hard	Stripe	Given an array of integers, find the first missing positive integer in linear time and constant space. In other words, find the lowest positive integer that does not exist in the array. The array can contain duplicates and negative numbers as well. For example, the input [3, 4, -1, 1] should give 2. The input [1, 2, 0] should give 3. You can modify the input array in-place.
3	binary tree serialization and deserialization	Medium	Google	Given the root to a binary tree, implement serialize(root), which serializes the tree into a string, and deserialize(s), which deserializes the string back into the tree. For example, given the following Node class class Node: def init(self, val, left=None, right=None): self.val = val self.left = left self.right = right The following test should pass: node = Node('root', Node('left', Node('left.left')), Node('right')) assert deserialize(serialize(node)).left.left.val == 'left.left'
2	product of other array elements	Hard	Uber	Given an array of integers, return a new array such that each element at index i of the new array is the product of all the numbers in the original array except the one at i. For example, if our input was [1, 2, 3, 4, 5], the expected output would be [120, 60, 40, 30, 24]. If our input was [3, 2, 1], the expected output would be [2, 3, 6]. Follow-up: what if you can't use division?
1	is sum in array	Easy	Google	Given a list of numbers and a number k, return whether any two numbers from the list add up to k. For example, given [10, 15, 3, 7] and k of 17, return true since 10 + 7 is 17. Bonus: Can you do this in one pass?