#bit manipulation

20 bit manipulation interview questions, asked at Amazon, Databricks, Microsoft and 11 more companies. Last asked Sep 2026.

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IPv4 range iterator with reverse and CIDR supportCodingAn IPv4 address such as "172.16.4.9" is four octets, each 0 to 255. Taken together, the octets form one unsigned 32-bit number. Build iterators that walk IPv4 addresses lazily…
Last asked Sep 2026
Maximize the bitwise AND of k elements with an increment budgetCodingYou get an array of non-negative integers, an integer k and a budget c. You may add amounts to elements as long as the total added over all elements is at most c. Then choose k…
Last asked Sep 2026
Ordered IP firewall with CIDR rulesCodingImplement an IPv4 firewall that checks addresses against an ordered list of rules. Each rule is a pair (action, target). action is "ALLOW" or "DENY". target is either a single…
Last asked Sep 2026
Fewest stones left after merging equal-level pairsCodingEach stone has a positive integer level. Two stones of the same level x can be merged into one stone of level x + 1, and merged stones can be merged again. Merging as much as you…
Last asked Sep 2026
Hybrid run-length and bit-packing codecCodingDesign an encoder and a decoder for a list of non-negative integers. The encoder compresses the list into a list of human-readable run strings. The decoder restores the original…
Last asked Aug 2026
XOR random number generator to encrypt and decrypt a treeCoding1. Implement a pseudo-random number generator whose state update uses bitwise XOR (shifts and XORs on an integer state), seeded so the same seed always gives the same sequence. 2…
Last asked Aug 2026
Count pairs of words with no letters in commonCodingGiven a list of strings, count the pairs that share no character. Encode each string's character set as a bitmask so a pair check is one AND, then group strings by mask to avoid…
Last asked Jul 2026
Maximum XOR productCodingGiven a, b and n, choose x with 0 <= x < 2^n to maximize (a XOR x) (b XOR x), returned modulo a large prime. Explain the bit-by-bit greedy that keeps the two factors as close as…
Last asked May 2026
Fewest powers of two to add or subtract to reach zeroCodingGiven a positive integer n, one operation adds or subtracts any power of two. Return the fewest operations that bring n to 0.
Last asked Feb 2026
Render, compress and invert a bitmap fontCodingA bitmap font is given as strings of 0 and 1 bits, one bitmap per character. 1. Render each character as a grid of text, with . for a 0 bit and another character for a 1 bit. 2…
Last asked Feb 2026
IP range to CIDR blocksCodingGiven a starting IPv4 address and a count n, return the shortest list of CIDR blocks that covers exactly the n consecutive addresses starting there, and no address outside that…
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
UTF-8 validationCodingGiven a list of integers, each standing for one byte, decide whether they form a valid UTF-8 encoding: read the leading bits of each first byte to know how many continuation bytes…
Last asked Sep 2025
Subsets, with and without backtrackingCodingReturn every subset of a set of distinct numbers using backtracking, then write it again iteratively, without backtracking, by building subsets up or using bit masks. Reported in…
Last asked Sep 2025
Find the number that appears an odd number of timesCodingIn an integer array exactly one value appears an odd number of times. Return it. A hash map is fine at first; the follow-up asks for O(1) extra space, which XOR gives.
Last asked Aug 2025
Set an even-parity bit in a byte's MSBCodingBytes sent over a noisy link often carry a parity bit so the receiver can detect a flipped bit. In this scheme the parity bit is the most significant bit (bit 7, value 128) and…
IP routing table with longest prefix matchCodingBuild the forwarding table of an IPv4 router. Routes are CIDR prefixes mapped to a next-hop name. When a packet arrives, the router must send it to the next hop of the most…
Largest subset with a non-zero bitwise ANDCodingGiven an array arr of positive integers, choose as many elements as you can so that the bitwise AND of all chosen elements is greater than 0. The chosen elements can come from…
Distinct OR values of increasing subsequencesCodingGiven an integer array arr, define the goodness of a sequence as the bitwise OR of all its elements. The goodness of the empty sequence is 0. A subsequence keeps elements in their…