Daily Coding Problems

My C++ solutions for the coding-interview-questions provided by Daily Coding Problem

Coding Problems Ordered by numbers:

Coding Problem #1 - [easy]
This Problem wasy recently asked by Google.
Given a list of numbers and a number k, return wheather any two numberrs from the list add up to k.

For example, given [10, 15, 3, 7] and k = 17, return true, since 10 + 7 = 17.

Bonus: Can you do this in one pass?

Coding Problem #2 - [hard]
This problem was asked by 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?

Coding Problem #3 - [medium]
This problem was asked by 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'

Coding Problem #4 - [hard]
This problem was asked by 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.

Coding Problem #5 - [medium]
This problem was asked by 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.

Coding Problem #6 - [hard]
This problem was asked by Google.
An XOR linked list is a more memory efficient doubly linked list. Instead of each node holding nextElement and prevElement fields, it holds a field named both, which is an XOR of the nextElement node and the previous node. Implement an XOR linked list; it has an add(node) which adds the node 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.

Coding Problem #7 - [medium]
This problem was asked by 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.

Coding Problem #8 - [easy]
This problem was asked by Google.
A unival root (which stands for "universal value") is a root where all nodes under it have the same value. Given the root to a binary root, count the number of unival subtrees.

For example, the following root has 5 unival subtrees:

Coding Problem #9 - [hard]
This problem was asked by 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?

Coding Problem #10 - [medium]
This problem was asked by Apple.
Implement a job scheduler which takes in a function f and an integer n, and calls f after n milliseconds.

Coding Problem #11 - [medium]
This problem was asked by 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.

Coding Problem #12 - [hard]
This problem was asked by 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.

Coding Problem #13 - [hard]
This problem was asked by 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".

Coding Problem #14 - [medium]
This problem was asked by Google.
The area of a circle is defined as πr². Estimate π to 3 decimal places using a Monte Carlo method.

Hint: The basic equation of a circle is x² + y² = r².

Coding Problem #15 - [medium]
This problem was asked by Facebook.
Given a stream of elements too large to store in memory, pick a random element from the stream with uniform probability.

Coding Problem #16 - [easy]
This problem was asked by 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.

Coding Problem #17 - [hard]
This problem was asked by 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.

Coding Problem #18 - [hard]
This problem was asked by Google.
Given an array of integers and a number k, where 1 <= k <= length of the array, compute the maximum values of each subarray of length k.

For example, given array = [10, 5, 2, 7, 8, 7] and k = 3, we should get: [10, 7, 8, 8], since:

10 = max(10, 5, 2)
7 = max(5, 2, 7)
8 = max(2, 7, 8)
8 = max(7, 8, 7)

Do this in O(n) time and O(k) space. You can modify the input array in-place and you do not need to store the results. You can simply print them out as you compute them.

Coding Problem #19 - [medium]
This problem was asked by Facebook.
A builder is looking to build a row of N houses that can be of K different colors. He has a goal of minimizing cost while ensuring that no two neighboring houses are of the same color. Given an N by K matrix where the n-th row and k-th column represents the cost to build the nth house with kth color, return the minimum cost which achieves this goal.

Coding Problem #20 - [easy]
This problem was asked by Google.
Given two singly linked lists that intersect at some point, find the intersecting node. The lists are non-cyclical. For example, given A = 3 -> 7 -> 8 -> 10 and B = 99 -> 1 -> 8 -> 10, return the node with value 8. In this example, assume nodes with the same value are the exact same node objects. Do this in O(M + N) time (where M and N are the lengths of the lists) and constant space.

AntonySJohn / Daily_Coding_Problems

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