Sum of numbers up to n divisible by 3, 5 or 7CodingGiven a positive integer n, return the sum of every integer from 1 to n that is divisible by at least one of 3, 5 and 7, counting each number once. A loop works; then do it in…
Last asked Sep 2026
#math
Path between two nodes of an implicit Fibonacci treeCodingA Fibonacci tree of order k is a binary tree defined recursively: - Orders 0 and 1 are a single node. - For k = 2, the root's left subtree is a Fibonacci tree of order k - 2 and…Last asked Sep 2026
Sort a transformed arrayCodingGiven a sorted array and the coefficients a, b, c of f(x) = ax^2 + bx + c, apply f to every element and return the results in sorted order in O(n). Use two pointers from both…Last asked Sep 2026- N-th number whose digits are all 3, 5 or 6CodingA good number is a positive integer whose decimal digits are all 3, 5 or 6: 3, 5, 6, 33, 35, 36, 53, ... Given n, return the n-th good number. Notice the link to counting in base…Last asked Sep 2026
Smallest larger number that shares no digit with nCodingGiven a positive integer n, return the smallest integer greater than n that contains none of the digits that appear in n, or -1 if there is none. Build the answer digit by digit…Last asked Sep 2026
+1Angle between clock handsCodingGiven a time in hours and minutes, return the smaller angle between the hour hand and the minute hand.Last asked Aug 2026
+1Can repeated pair additions reach a target pointCodingFrom a starting point (x, y) you may move to (x + y, y) or (x, x + y). Decide whether a target point is reachable, efficiently even for very large coordinates.Last asked Jul 2026
Monotone increasing digitsCoding1. Check whether a number's digits never decrease from left to right. 2. Given n, return the largest number no greater than n whose digits never decrease.Last asked Jul 2026
Roman numeral to integerCodingConvert a Roman numeral string to an integer. Add each symbol's value, except subtract it when a smaller value comes right before a larger one (as in IV or CM). Discuss how you…Last asked Jun 2026
+1Next greater palindromeCodingYou are given a string n holding a positive integer in decimal, with no leading zeros. It can be hundreds of digits long, so it may not fit in any built-in integer type. Return…Last asked Jun 2026- +1Maximize pipeline throughput within a scaling budgetCodingA message pipeline has n services in series, and every message passes through all of them. The pipeline's throughput is therefore the minimum throughput of any service. You are…Last asked Jun 2026
- Sort an array with rotate and flip operationsCodingYou are given an array arr of n distinct integers. You may apply two operations, and each one counts as one step: - Rotate: remove the first element and append it to the end. p…Last asked May 2026
- +1Best meeting point on a gridCodingA grid marks several people's (or points') positions. Find the cell that minimizes the total distance to all of them. Start with a brute force (for example a BFS from each point)…Last asked May 2026
Count ways to write N as a sum of consecutive positive integersCodingGiven n, count how many ways it can be written as a sum of one or more consecutive positive integers. A run of k numbers starting at a sums to ka + k(k-1)/2, so try each k while…Last asked Apr 2026
Implement pow(x, n)CodingCompute x raised to an integer power n (which may be negative) in O(log n) multiplications by squaring, rather than multiplying n times. Handle n = 0, negative exponents and…Last asked Apr 2026- Palindrome number and merge intervalsCodingTwo short problems: 1. Decide whether an integer reads the same forwards and backwards. 2. Merge a list of possibly overlapping ranges into the fewest non-overlapping ranges.Last asked Mar 2026
- Squirrel carrying nuts to a treeCodingA squirrel, a tree and several nuts are on a grid. The squirrel carries one nut at a time to the tree, moving one cell up, down, left or right per step. Return the fewest moves to…Last asked Mar 2026
- Lift-to-stairs switch with an energy budgetCodingYou start on floor 0 of a building with 0 energy and need to reach floor n. You ride the lift from floor 0 up to some floor k (0 <= k <= n), then walk the stairs from floor k to…Last asked Feb 2026
Intersection of two line segmentsCodingGiven two line segments in the plane, each by its two endpoints, decide whether they intersect and return the intersection point (or the overlapping piece when they are collinear…Last asked Feb 2026
Max points on a lineCodingGiven points on a plane, return the largest number of them that lie on one straight line. Explain how you represent slopes exactly (reduced fractions, not floats) and handle…Last asked Feb 2026- Find the nth primeCodingReturn the nth prime number. Start with trial division, then use a sieve of Eratosthenes with an estimated upper bound and explain the complexity of both.Last asked Feb 2026
Pick the most profitable repeated queryCodingA data warehouse has a time budget of k minutes and n query types. Query type i takes timesi minutes per run and earns profitsi per completed run. You must commit to one query…Last asked Jan 2026- Count three-digit numbers with distinct digitsCodingCount the three-digit numbers whose digits are all different, first by brute force and then by counting directly.Last asked Jan 2026
- Add two binary stringsCodingGiven two binary numbers as strings, return their sum as a binary string, adding digit by digit from the right with a carry, without converting to integers.Last asked Jan 2026
- Convert an integer to hexadecimalCodingConvert a 32-bit signed integer to a lowercase hexadecimal string without library conversion functions. Negative numbers use two's complement, and the result has no leading zeros…Last asked Dec 2025
- Divide two integers without divisionCodingDivide two integers without using multiplication, division or the modulo operator, truncating toward zero. Do better than subtracting the divisor one copy at a time by doubling it…Last asked Dec 2025
- Add two big integers stored as digit listsCodingTwo non-negative integers too large for built-in types are given as lists of digits. Return their sum in the same form. Handle different lengths and the final carry, and say how…Last asked Nov 2025
- Count pairs with 1/x + 1/y = 1/NCodingGiven a positive integer N up to about a million, count the ordered pairs of positive integers (x, y) with 1/x + 1/y = 1/N. Show that the count equals the number of divisors of…Last asked Nov 2025
- Happy numberCodingReplace a number with the sum of the squares of its digits and repeat. Return whether it reaches 1 or loops forever. Detect the loop with a set of seen values or with fast and…Last asked Oct 2025
- Numbers that are a sum of two squares in exactly two waysCodingFind the numbers up to a limit that can be written as a^2 + b^2 in exactly two different ways (unordered, with the agreed rule on zero). Enumerate pairs efficiently, count…Last asked Oct 2025
- Unload warehouses in turns with limited skipsCodingYou and a co-worker empty warehouses one at a time; warehouse i holds ci items. You take turns: you remove m items per turn and your co-worker removes n. You earn a point for a…Last asked Sep 2025
- Most distinct values of B[i] mod A[i]CodingYou get an array A of n positive integers. You choose any array B of length n, and compute Bi % Ai for every i. Return the largest possible number of distinct values among these…Last asked Sep 2025
Sum of products over all subarraysCodingAn online assessment with two problems. 1. A simplified text justification: lay words out into lines of a fixed width. 2. Given an array, return the sum, over every contiguous…Last asked Aug 2025- Add two decimal number stringsCodingAdd two non-negative numbers given as strings and return the sum as a string, digit by digit with a carry. Then support a decimal point: pad the fractional parts to the same…Last asked Jul 2025
- Multiply stringsCodingMultiply two non-negative integers given as strings and return the product as a string, without converting them to built-in big integers. Use grade-school multiplication into an…Last asked Jul 2025
- Maximum swapCodingGiven a non-negative integer, swap two of its digits at most once to make the largest number possible. Record the last position of each digit, then find the first digit that has a…Last asked Jul 2025
- N-th license plate in sorted orderCodingLicense plates follow a fixed format, for example three letters A-Z then three digits 0-9 (AAA000). Sorted in dictionary order, what is the n-th plate? Compute it directly by…Last asked Jun 2025
Multiples streamCodingGenerate the infinite stream of multiples (or Hamming-like numbers) lazily, yielding values in order on demand. Reported on 1point3acres' Sierra bank; reconstructed in our own…- Count valid 24-hour times from four digitsCodingWrite a function countvalidtimes(a, b, c, d) that takes four digits (each an integer from 0 to 9). Arrange all four digits as HH:MM on a 24-hour clock, using each given digit…
- Pascal triangle digit encryptionCodingDigits are encrypted by folding them down an upside-down Pascal's triangle. You get a list of n digits (each 0-9). In one round, replace the list with the sums of each pair of…
- Minimum cost to clear a binary array with k-wide windowsCodingA packaging line tracks a row of n units, each built as one of two variants: variant A is written 0 and variant B is written 1. You need to convert every unit to variant A. You…
- Best single location on a line to minimize total distanceCodingYou are choosing one location on a number line to serve a set of sites. You are given a non-empty integer array nums. Each value is the coordinate of a site (values may repeat and…
- +2Fewest coins that cover every amount up to a limitCodingYou are given a list of coin denominations (positive integers) and an integer maxamount. You may take any number of coins of each denomination. Choose a multiset of coins so that…
- Best k-day run in a cyclic sprint scheduleCodingA training program is made of n back-to-back sprints. Sprint i lasts daysi days. On day j of a sprint (counting from 1 within that sprint), finishing that day's work earns j…
- Largest square from 1x1 and 2x2 tilesCodingYou have M small tiles of size 1×1 and N large tiles of size 2×2. Build the largest possible square: every cell of the square must be covered by exactly one tile, with no gaps, no…
- Integer to English words, built up by rangeCodingWrite a function that spells out an integer in English words. The interviewer adds the ranges in parts, and later parts should reuse earlier ones, so design for extension from the…
- Days needed to finish recurring tasksCodingYou run n recurring tasks. Task i runs for the first time on day 1 and then again every intervalsi days, so it runs on days 1, 1 + intervalsi, 1 + 2 intervalsi, .... Any number of…
- Count colorings of a row of houses with fixed end colorsCodingA contractor is repainting a row of n houses, numbered 0 to n - 1. There are k paint colors, numbered 0 to k - 1. The new paint job must follow two rules: - Two neighboring houses…
- Collatz sequence steps with memoized range maximumCodingStarting from a positive integer n, repeat the following until n equals 1: - If n is even, set n = n / 2. - If n is odd, set n = 3n + 1. Each replacement counts as one step. (It…
- ATM queue exit orderCodingThere are n people waiting in a single line at an ATM. They are numbered 1 to n from the front of the line to the back. You are given an integer array amounts, where amountsi is…