Day 25
Implement regular expression matching with the following special characters:
- . (period) which matches any single character
-
- (asterisk) which matches zero or more of the preceding element
That is, implement a function that takes in a string and a valid regular expression and returns whether or not the string matches the regular expression.
For example, given the regular expression "ra." and the string "ray", your function should return true. The same regular expression on the string "raymond" should return false.
Given the regular expression ".*at" and the string "chat", your function should return true. The same regular expression on the string "chats" should return false.
This problem was asked by Facebook.
Day 26
Given a singly linked list and an integer k, remove the kth last element from the list. k is guaranteed to be smaller than the length of the list.
The list is very long, so making more than one pass is prohibitively expensive. Do this in constant space and in one pass.
This problem was asked by Google.
Day 27
Given a string of round, curly, and square open and closing brackets, return whether the brackets are balanced (well-formed). For example, given the string "([])", you should return true.
Given the string "([)]" or "((()", you should return false.
This problem was asked by Facebook.
Day 28
Write an algorithm to justify text. Given a sequence of words and an integer line length k, return a list of strings which represents each line, fully justified.
More specifically, you should have as many words as possible in each line. There should be at least one space between each word. Pad extra spaces when necessary so that each line has exactly length k. Spaces should be distributed as equally as possible, with the extra spaces, if any, distributed starting from the left.
If you can only fit one word on a line, then you should pad the right-hand side with spaces. Each word is guaranteed not to be longer than k.
For example, given the list of words
["the", "quick", "brown", "fox", "jumps", "over", "the", "lazy", "dog"] and k = 16, you should return the following:
["the quick brown", # 1 extra space on the left
"fox jumps over", # 2 extra spaces distributed evenly
"the lazy dog"] # 4 extra spaces distributed evenly
This problem was asked by Palantir.
Day 29
Run-length encoding is a fast and simple method of encoding strings. The basic idea is to represent repeated successive characters as a single count and character. For example, the string "AAAABBBCCDAA" would be encoded as "4A3B2C1D2A".
Implement run-length encoding and decoding. You can assume the string to be encoded have no digits and consists solely of alphabetic characters. You can assume the string to be decoded is valid.
This problem was asked by Amazon.
Day 30
You are given an array of non-negative integers that represents a two-dimensional elevation map where each element is unit-width wall and the integer is the height.
Suppose it will rain and all spots between two walls get filled up. Compute how many units of water remain trapped on the map in O(N) time and O(1) space.
For example, given the input [2, 1, 2], we can hold 1 unit of water in the middle.
Given the input [3, 0, 1, 3, 0, 5], we can hold 3 units in the first index, 2 in the second, and 3 in the fourth index (we cannot hold 5 since it would run off to the left), so we can trap 8 units of water.
This problem was asked by Facebook.
Day 31
The edit distance between two strings refers to the minimum number of character insertions, deletions, and substitutions required to change one string to the other. For example, the edit distance between “kitten” and “sitting” is three: substitute the 'k' for 's', substitute the 'e' for 'i', and append a 'g'.
Given two strings, compute the edit distance between them.
This problem was asked by Google.
Day 32
Suppose you are given a table of currency exchange rates, represented as a 2D array. Determine whether there is a possible arbitrage: that is, whether there is some sequence of trades you can make, starting with some amount A of any currency, so that you can end up with some amount greater than A of that currency.
There are no transaction costs and you can trade fractional quantities.
This problem was asked by Jane Street.
Day 33
Compute the running median of a sequence of numbers. That is, given a stream of numbers, print out the median of the list so far on each new element. Recall that the median of an even-numbered list is the average of the two middle numbers.
For example, given the sequence [2, 1, 5, 7, 2, 0, 5], your algorithm should
print out:
2
1.5
2
3.5
2
2
2
This problem was asked by Microsoft.
Day 34
Given a string, find the palindrome that can be made by inserting the fewest number of characters as possible anywhere in the word. If there is more than one palindrome of minimum length that can be made, return the lexicographically earliest one (the first one alphabetically).
For example, given the string "race", you should return "ecarace", since we can add three letters to it (which is the smallest amount to make a palindrome). There are seven other palindromes that can be made from "race" by adding three letters, but "ecarace" comes first alphabetically.
As another example, given the string "google", you should return "elgoogle".
This problem was asked by Quora.
Day 35
Given an array of strictly the characters 'R', 'G', and 'B', segregate the values of the array so that all the Rs come first, the Gs come second, and the Bs come last. You can only swap elements of the array.
Do this in linear time and in-place.
For example, given the array ['G', 'B', 'R', 'R', 'B', 'R', 'G'], it should become ['R', 'R', 'R', 'G', 'G', 'B', 'B'].
This problem was asked by Google.
Day 36
Given the root to a binary search tree, find the second largest node in the tree.
This problem was asked by Dropbox.
Day 37
The power set of a set is the set of all its subsets. Write a function that, given a set, generates its power set.
For example, given the set {1, 2, 3}, it should return {{}, {1}, {2}, {3}, {1, 2}, {1, 3}, {2, 3}, {1, 2, 3}}.
You may also use a list or array to represent a set.
This problem was asked by Google.
Day 38
You have an N by N board. Write a function that, given N, returns the number of possible arrangements of the board where N queens can be placed on the board without threatening each other, i.e. no two queens share the same row, column, or diagonal.
This problem was asked by Microsoft.
Day 39
Conway's Game of Life takes place on an infinite two-dimensional board of square cells. Each cell is either dead or alive, and at each tick, the following rules apply:
- Any live cell with less than two live neighbours dies.
- Any live cell with two or three live neighbours remains living.
- Any live cell with more than three live neighbours dies.
- Any dead cell with exactly three live neighbours becomes a live cell.
- A cell neighbours another cell if it is horizontally, vertically, or diagonally adjacent.
Implement Conway's Game of Life. It should be able to be initialized with a starting list of live cell coordinates and the number of steps it should run for. Once initialized, it should print out the board state at each step. Since it's an infinite board, print out only the relevant coordinates, i.e. from the top-leftmost live cell to bottom-rightmost live cell.
You can represent a live cell with an asterisk (*) and a dead cell with a dot (.).
This problem was asked by Dropbox.
Day 40
Given an array of integers where every integer occurs three times except for one integer, which only occurs once, find and return the non-duplicated integer.
For example, given [6, 1, 3, 3, 3, 6, 6], return 1. Given [13, 19, 13, 13], return 19.
Do this in O(N) time and O(1) space.
This problem was asked by Google.
Day 41
Given an unordered list of flights taken by someone, each represented as (origin, destination) pairs, and a starting airport, compute the person's itinerary. If no such itinerary exists, return null. If there are multiple possible itineraries, return the lexicographically smallest one. All flights must be used in the itinerary.
For example, given the list of flights [('SFO', 'HKO'), ('YYZ', 'SFO'), ('YUL', 'YYZ'), ('HKO', 'ORD')] and starting airport 'YUL', you should return the list ['YUL', 'YYZ', 'SFO', 'HKO', 'ORD'].
Given the list of flights [('SFO', 'COM'), ('COM', 'YYZ')] and starting airport 'COM', you should return null.
Given the list of flights [('A', 'B'), ('A', 'C'), ('B', 'C'), ('C', 'A')] and starting airport 'A', you should return the list ['A', 'B', 'C', 'A', 'C'] even though ['A', 'C', 'A', 'B', 'C'] is also a valid itinerary. However, the first one is lexicographically smaller.
This problem was asked by Facebook.
Day 42
Given a list of integers S and a target number k, write a function that returns a subset of S that adds up to k.
If such a subset cannot be made, then return null.
Integers can appear more than once in the list. You may assume all numbers in the list are positive.
For example, given S = [12, 1, 61, 5, 9, 2] and k = 24, return [12, 9, 2, 1] since it sums up to 24.
This problem was asked by Google.
Day 43
Implement a stack that has the following methods:
- push(val), which pushes an element onto the stack
- pop(), which pops off and returns the topmost element of the stack. If there are no elements in the stack, then it should throw an error or return null.
- max(), which returns the maximum value in the stack currently. If there are no elements in the stack, then it should throw an error or return null.
Each method should run in constant time.
This problem was asked by Amazon.
Day 44
We can determine how "out of order" an array A is by counting the number of inversions it has. Two elements A[i] and A[j] form an inversion if A[i] > A[j] but i < j. That is, a smaller element appears after a larger element.
Given an array, count the number of inversions it has. Do this faster than O(N^2) time.
You may assume each element in the array is distinct.
For example, a sorted list has zero inversions. The array [2, 4, 1, 3, 5] has three inversions: (2, 1), (4, 1), and (4, 3).
The array [5, 4, 3, 2, 1] has ten inversions: every distinct pair forms an inversion.
This problem was asked by Google.
Day 45
Using a function rand5() that returns an integer from 1 to 5 (inclusive) with uniform probability, implement a function rand7() that returns an integer from 1 to 7 (inclusive).
This problem was asked by Two Sigma.
Day 46
Given a string, find the longest palindromic contiguous substring. If there are more than one with the maximum length, return any one.
For example, the longest palindromic substring of "aabcdcb" is "bcdcb". The longest palindromic substring of "bananas" is "anana". """ This problem was asked by Amazon.
Day 47
Given a array of numbers representing the stock prices of a company in chronological order, write a function that calculates the maximum profit you could have made from buying and selling that stock once. You must buy before you can sell it.
For example, given [9, 11, 8, 5, 7, 10], you should return 5, since you could buy the stock at 5 dollars and sell it at 10 dollars.
This problem was asked by Facebook.
Day 48
Given pre-order and in-order traversals of a binary tree, write a function to reconstruct the tree.
For example, given the following preorder traversal:
[a, b, d, e, c, f, g]
And the following inorder traversal:
[d, b, e, a, f, c, g]
You should return the following tree:
a
/ \
b c
/ \ / \
d e f g
This problem was asked by Google.
Day 49
Given an array of numbers, find the maximum sum of any contiguous subarray of the array.
For example, given the array [34, -50, 42, 14, -5, 86], the maximum sum would be 137, since we would take elements 42, 14, -5, and 86.
Given the array [-5, -1, -8, -9], the maximum sum would be 0, since we would not take any elements.
Do this in O(N) time.
This problem was asked by Amazon.
Day 50
Suppose an arithmetic expression is given as a binary tree. Each leaf is an integer and each internal node is one of '+', '−', '∗', or '/'.
Given the root to such a tree, write a function to evaluate it.
For example, given the following tree:
*
/ \
+ +
/ \ / \
3 2 4 5
You should return 45, as it is (3 + 2) * (4 + 5).
This problem was asked by Microsoft.
Day 51
Given a function that generates perfectly random numbers between 1 and k (inclusive), where k is an input, write a function that shuffles a deck of cards represented as an array using only swaps.
It should run in O(N) time.
Hint: Make sure each one of the 52! permutations of the deck is equally likely.
This problem was asked by Facebook.
Day 52
Implement an LRU (Least Recently Used) cache. It should be able to be initialized with a cache size n, and contain the following methods:
- set(key, value): sets key to value. If there are already n items in the cache and we are adding a new item, then it should also remove the least recently used item.
- get(key): gets the value at key. If no such key exists, return null.
Each operation should run in O(1) time.
This problem was asked by Google.
Day 53
Implement a queue using two stacks. Recall that a queue is a FIFO (first-in, first-out) data structure with the following methods: enqueue, which inserts an element into the queue, and dequeue, which removes it.
This problem was asked by Apple.
Day 54
Sudoku is a puzzle where you're given a partially-filled 9 by 9 grid with digits. The objective is to fill the grid with the constraint that every row, column, and box (3 by 3 subgrid) must contain all of the digits from 1 to 9.
Implement an efficient sudoku solver.
This problem was asked by Dropbox.
Day 55
Implement a URL shortener with the following methods:
- shorten(url), which shortens the url into a six-character alphanumeric string, such as zLg6wl.
- restore(short), which expands the shortened string into the original url. If no such shortened string exists, return null.
Hint: What if we enter the same URL twice?
This problem was asked by Microsoft.
Day 56
Given an undirected graph represented as an adjacency matrix and an integer k, write a function to determine whether each vertex in the graph can be colored such that no two adjacent vertices share the same color using at most k colors.
This problem was asked by Google.
Day 57
Given a string s and an integer k, break up the string into multiple texts such that each text has a length of k or less. You must break it up so that words don't break across lines. If there's no way to break the text up, then return null.
You can assume that there are no spaces at the ends of the string and that there is exactly one space between each word.
For example, given the string "the quick brown fox jumps over the lazy dog" and k = 10, you should return: ["the quick", "brown fox", "jumps over", "the lazy", "dog"]. No string in the list has a length of more than 10.
This problem was asked by Amazon.
Day 58
An sorted array of integers was rotated an unknown number of times.
Given such an array, find the index of the element in the array in faster than linear time. If the element doesn't exist in the array, return null.
For example, given the array [13, 18, 25, 2, 8, 10] and the element 8, return 4 (the index of 8 in the array).
You can assume all the integers in the array are unique.
This problem was asked by Amazon.
Day 59
Implement a file syncing algorithm for two computers over a low-bandwidth network. What if we know the files in the two computers are mostly the same?
This problem was asked by Google.
Day 60
Given a multiset of integers, return whether it can be partitioned into two subsets whose sums are the same.
For example, given the multiset {15, 5, 20, 10, 35, 15, 10}, it would return true, since we can split it up into {15, 5, 10, 15, 10} and {20, 35}, which both add up to 55.
Given the multiset {15, 5, 20, 10, 35}, it would return false, since we can't split it up into two subsets that add up to the same sum.
This problem was asked by Facebook.
Day 61
Implement integer exponentiation. That is, implement the pow(x, y) function, where x and y are integers and returns x^y.
Do this faster than the naive method of repeated multiplication.
For example, pow(2, 10) should return 1024.
This problem was asked by Google.
Day 62
There is an N by M matrix of zeroes. Given N and M, write a function to count the number of ways of starting at the top-left corner and getting to the bottom-right corner. You can only move right or down.
For example, given a 2 by 2 matrix, you should return 2, since there are two ways to get to the bottom-right:
- Right, then down
- Down, then right
Given a 5 by 5 matrix, there are 70 ways to get to the bottom-right.
This problem was asked by Facebook.
Day 63
Given a 2D matrix of characters and a target word, write a function that returns whether the word can be found in the matrix by going left-to-right, or up-to-down.
For example, given the following matrix:
[['F', 'A', 'C', 'I'],
['O', 'B', 'Q', 'P'],
['A', 'N', 'O', 'B'],
['M', 'A', 'S', 'S']]
and the target word 'FOAM', you should return true, since it's the leftmost column. Similarly, given the target word 'MASS', you should return true, since it's the last row.
This problem was asked by Microsoft.
Day 64
A knight's tour is a sequence of moves by a knight on a chessboard such that all squares are visited once.
Given N, write a function to return the number of knight's tours on an N by N chessboard.
This problem was asked by Google.
Day 65
Given a N by M matrix of numbers, print out the matrix in a clockwise spiral.
For example, given the following matrix:
[[1, 2, 3, 4, 5],
[6, 7, 8, 9, 10],
[11, 12, 13, 14, 15],
[16, 17, 18, 19, 20]]
You should print out the following:
1
2
3
4
5
10
15
20
19
18
17
16
11
6
7
8
9
14
13
12
Upgrade to premium and get in-depth solutions to every problem. Since you were referred by one of our affiliates, you'll get a 10% discount on checkout!
This problem was asked by Amazon.
Day 66
Assume you have access to a function toss_biased() which returns 0 or 1 with a probability that's not 50-50 (but also not 0-100 or 100-0). You do not know the bias of the coin.
Write a function to simulate an unbiased coin toss.
This problem was asked by Square.
Day 67
Implement an LFU (Least Frequently Used) cache. It should be able to be initialized with a cache size n, and contain the following methods:
- set(key, value): sets key to value. If there are already n items in the cache and we are adding a new item, then it should also remove the least frequently used item. If there is a tie, then the least recently used key should be removed.
- get(key): gets the value at key. If no such key exists, return null. Each operation should run in O(1) time.
This problem was asked by Google.
Day 68
On our special chessboard, two bishops attack each other if they share the same diagonal. This includes bishops that have another bishop located between them, i.e. bishops can attack through pieces.
You are given N bishops, represented as (row, column) tuples on a M by M chessboard. Write a function to count the number of pairs of bishops that attack each other. The ordering of the pair doesn't matter: (1, 2) is considered the same as (2, 1).
For example, given M = 5 and the list of bishops:
(0, 0)
(1, 2)
(2, 2)
(4, 0)
The board would look like this:
[b 0 0 0 0]
[0 0 b 0 0]
[0 0 b 0 0]
[0 0 0 0 0]
[b 0 0 0 0]
You should return 2, since bishops 1 and 3 attack each other, as well as bishops 3 and 4.
This problem was asked by Google.
Day 69
Given a list of integers, return the largest product that can be made by multiplying any three integers.
For example, if the list is [-10, -10, 5, 2], we should return 500, since that's -10 * -10 * 5.
You can assume the list has at least three integers.
This problem was asked by Facebook.
Day 70
A number is considered perfect if its digits sum up to exactly 10.
Given a positive integer n, return the n-th perfect number.
For example, given 1, you should return 19. Given 2, you should return 28.
This problem was asked by Microsoft.
Day 71
Using a function rand7() that returns an integer from 1 to 7 (inclusive) with uniform probability, implement a function rand5() that returns an integer from 1 to 5 (inclusive).
This problem was asked by Two Sigma.
Day 72
In a directed graph, each node is assigned an uppercase letter. We define a path's value as the number of most frequently-occurring letter along that path. For example, if a path in the graph goes through "ABACA", the value of the path is 3, since there are 3 occurrences of 'A' on the path.
Given a graph with n nodes and m directed edges, return the largest value path of the graph. If the largest value is infinite, then return null.
The graph is represented with a string and an edge list. The i-th character represents the uppercase letter of the i-th node. Each tuple in the edge list (i, j) means there is a directed edge from the i-th node to the j-th node. Self-edges are possible, as well as multi-edges.
For example, the following input graph:
ABACA
[(0, 1),
(0, 2),
(2, 3),
(3, 4)]
Would have maximum value 3 using the path of vertices [0, 2, 3, 4], (A, A, C, A).
The following input graph:
A
[(0, 0)]
Should return null, since we have an infinite loop.
This problem was asked by Google.
Day 73
Given the head of a singly linked list, reverse it in-place.
This problem was asked by Google.
Day 74
Suppose you have a multiplication table that is N by N. That is, a 2D array where the value at the i-th row and j-th column is (i + 1) * (j + 1) (if 0-indexed) or i * j (if 1-indexed).
Given integers N and X, write a function that returns the number of times X appears as a value in an N by N multiplication table.
For example, given N = 6 and X = 12, you should return 4, since the multiplication table looks like this:
| 1 | 2 | 3 | 4 | 5 | 6 |
| 2 | 4 | 6 | 8 | 10 | 12 |
| 3 | 6 | 9 | 12 | 15 | 18 |
| 4 | 8 | 12 | 16 | 20 | 24 |
| 5 | 10 | 15 | 20 | 25 | 30 |
| 6 | 12 | 18 | 24 | 30 | 36 |
And there are 4 12's in the table.
This problem was asked by Apple.
Day 75
Given an array of numbers, find the length of the longest increasing subsequence in the array. The subsequence does not necessarily have to be contiguous.
For example, given the array [0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15], the longest increasing subsequence has length 6: it is 0, 2, 6, 9, 11, 15.
This problem was asked by Microsoft.
Day 76
You are given an N by M 2D matrix of lowercase letters. Determine the minimum number of columns that can be removed to ensure that each row is ordered from top to bottom lexicographically. That is, the letter at each column is lexicographically later as you go down each row. It does not matter whether each row itself is ordered lexicographically.
For example, given the following table:
cba
daf
ghi
This is not ordered because of the a in the center. We can remove the second column to make it ordered:
ca
df
gi
So your function should return 1, since we only needed to remove 1 column.
As another example, given the following table:
abcdef
Your function should return 0, since the rows are already ordered (there's only one row).
As another example, given the following table:
zyx
wvu
tsr
Your function should return 3, since we would need to remove all the columns to order it.
This problem was asked by Google.
Day 77
Given a list of possibly overlapping intervals, return a new list of intervals where all overlapping intervals have been merged.
The input list is not necessarily ordered in any way.
For example, given [(1, 3), (5, 8), (4, 10), (20, 25)], you should return [(1, 3), (4, 10), (20, 25)].
This problem was asked by Snapchat.
Day 78
Given k sorted singly linked lists, write a function to merge all the lists into one sorted singly linked list.
This problem was asked recently by Google.
Day 79
Given an array of integers, write a function to determine whether the array could become non-decreasing by modifying at most 1 element.
For example, given the array [10, 5, 7], you should return true, since we can modify the 10 into a 1 to make the array non-decreasing.
Given the array [10, 5, 1], you should return false, since we can't modify any one element to get a non-decreasing array.
This problem was asked by Facebook.
Day 80
Given the root of a binary tree, return a deepest node. For example, in the following tree, return d.
a
/ \
b c
/
d
This problem was asked by Google.
Day 81
Given a mapping of digits to letters (as in a phone number), and a digit string, return all possible letters the number could represent. You can assume each valid number in the mapping is a single digit.
For example if {“2”: [“a”, “b”, “c”], 3: [“d”, “e”, “f”], …} then “23” should return [“ad”, “ae”, “af”, “bd”, “be”, “bf”, “cd”, “ce”, “cf"].
This problem was asked by Yelp.
Day 82
This problem was asked Microsoft.
Using a read7() method that returns 7 characters from a file, implement readN(n) which reads n characters.
For example, given a file with the content “Hello world”, three read7() returns “Hello w”, “orld” and then “”.
This problem was asked Microsoft.
Day 83
Invert a binary tree.
For example, given the following tree:
a
/ \
b c
/ \ /
d e f
should become:
a
/ \
c b
\ / \
f e d
This problem was asked by Google.
Day 84
Given a matrix of 1s and 0s, return the number of "islands" in the matrix. A 1 represents land and 0 represents water, so an island is a group of 1s that are neighboring and their perimiter is surrounded by water.
For example, this matrix has 4 islands.
1 0 0 0 0
0 0 1 1 0
0 1 1 0 0
0 0 0 0 0
1 1 0 0 1
1 1 0 0 1
This problem was asked by Amazon.
Day 85
Given three 32-bit integers x, y, and b, return x if b is 1 and y if b is 0, using only mathematical or bit operations. You can assume b can only be 1 or 0.
This problem was asked by Facebook.
Day 86
Given a string of parentheses, write a function to compute the minimum number of parentheses to be removed to make the string valid (i.e. each open parenthesis is eventually closed).
For example, given the string "()())()", you should return 1. Given the string ")(", you should return 2, since we must remove all of them.
This problem was asked by Google.
Day 87
A rule looks like this:
A NE B
This means this means point A is located northeast of point B.
A SW C
means that point A is southwest of C.
Given a list of rules, check if the sum of the rules validate. For example:
A N B B NE C C N A does not validate, since A cannot be both north and south of C.
A NW B A N B is considered valid.
This problem was asked by Uber.
Day 88
Implement division of two positive integers without using the division, multiplication, or modulus operators. Return the quotient as an integer, ignoring the remainder.
This question was asked by ContextLogic.
Day 89
Determine whether a tree is a valid binary search tree.
A binary search tree is a tree with two children, left and right, and satisfies the constraint that the key in the left child must be less than or equal to the root and the key in the right child must be greater than or equal to the root.
This problem was asked by LinkedIn.
Day 90
Given an integer n and a list of integers l, write a function that randomly generates a number from 0 to n-1 that isn't in l (uniform).
This question was asked by Google.
Day 91
What does the below code snippet print out? How can we fix the anonymous functions to behave as we'd expect?
functions = []
for i in range(10):
functions.append(lambda : i)
for f in functions:
print(f())
This problem was asked by Dropbox.
Day 92
We're given a hashmap with a key courseId and value a list of courseIds, which represents that the prerequsite of courseId is courseIds. Return a sorted ordering of courses such that we can finish all courses.
Return null if there is no such ordering.
For example, given {'CSC300': ['CSC100', 'CSC200'], 'CSC200': ['CSC100'], 'CSC100': []}, should return ['CSC100', 'CSC200', 'CSCS300'].
This problem was asked by Airbnb.
Day 93
Given a tree, find the largest tree/subtree that is a BST.
Given a tree, return the size of the largest tree/subtree that is a BST.
This problem was asked by Apple.
Day 94
Given a binary tree of integers, find the maximum path sum between two nodes. The path must go through at least one node, and does not need to go through the root.
This problem was asked by Google.
Day 95
Given a number represented by a list of digits, find the next greater permutation of a number, in terms of lexicographic ordering. If there is not greater permutation possible, return the permutation with the lowest value/ordering.
For example, the list [1,2,3] should return [1,3,2]. The list [1,3,2] should return [2,1,3]. The list [3,2,1] should return [1,2,3].
Can you perform the operation without allocating extra memory (disregarding the input memory)?
This problem was asked by Palantir.
Day 96
Given a number in the form of a list of digits, return all possible permutations.
For example, given [1,2,3], return [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]].
This problem was asked by Microsoft.
Day 97
Write a map implementation with a get function that lets you retrieve the value of a key at a particular time.
It should contain the following methods:
- set(key, value, time): sets key to value for t = time.
- get(key, time): gets the key at t = time.
The map should work like this. If we set a key at a particular time, it will maintain that value forever or until it gets set at a later time. In other words, when we get a key at a time, it should return the value that was set for that key set at the most recent time.
Consider the following examples:
d.set(1, 1, 0) # set key 1 to value 1 at time 0
d.set(1, 2, 2) # set key 1 to value 2 at time 2
d.get(1, 1) # get key 1 at time 1 should be 1
d.get(1, 3) # get key 1 at time 3 should be 2
d.set(1, 1, 5) # set key 1 to value 1 at time 5
d.get(1, 0) # get key 1 at time 0 should be null
d.get(1, 10) # get key 1 at time 10 should be 1
d.set(1, 1, 0) # set key 1 to value 1 at time 0
d.set(1, 2, 0) # set key 1 to value 2 at time 0
d.get(1, 0) # get key 1 at time 0 should be 2
This problem was asked by Stripe.
Day 98
Given a 2D board of characters and a word, find if the word exists in the grid.
The word can be constructed from letters of sequentially adjacent cell, where "adjacent" cells are those horizontally or vertically neighboring. The same letter cell may not be used more than once.
For example, given the following board:
[
['A','B','C','E'],
['S','F','C','S'],
['A','D','E','E']
]
exists(board, "ABCCED") returns true, exists(board, "SEE") returns true, exists(board, "ABCB") returns false.
This problem was asked by Coursera.
Day 99
Given an unsorted array of integers, find the length of the longest consecutive elements sequence.
For example, given [100, 4, 200, 1, 3, 2], the longest consecutive element sequence is [1, 2, 3, 4]. Return its length: 4.
Your algorithm should run in O(n) complexity.
This problem was asked by Microsoft.
Day 100
You are in an infinite 2D grid where you can move in any of the 8 directions:
(x,y) to
(x+1, y),
(x - 1, y),
(x, y+1),
(x, y-1),
(x-1, y-1),
(x+1,y+1),
(x-1,y+1),
(x+1,y-1)
You are given a sequence of points and the order in which you need to cover the points. Give the minimum number of steps in which you can achieve it. You start from the first point.
Example:
Input: [(0, 0), (1, 1), (1, 2)]
Output: 2
It takes 1 step to move from (0, 0) to (1, 1). It takes one more step to move from (1, 1) to (1, 2).
This problem was asked by Google.