Interview questions

Count Evenly Good Integers

General practice

Count Fancy Numbers in a Range

General practice

Count Fertile Pyramids in a Land

Given an m x n binary grid, count all upward- and downward-pointing isosceles triangular regions made entirely of 1s (pyramids/inverse pyramids) with height > 1…

General practice

Count Frequency Staircase Subarrays I

General practice

Count Frequency Staircase Subarrays II

General practice

Count Good Cyclic Rotations

General practice

Count Good Integers in a Range

General practice

Count Good Integers on a Grid Path

General practice

Count Good Meals

Count the number of index pairs (i<j) in an array whose values sum to a power of two, returning the result modulo 1e9+7. The challenge…

General practice

Count Good Numbers

Count the number of length-n digit strings where digits at even indices must be even (5 choices) and digits at odd indices must be prime…

General practice

Count Good Strings

General practice

Count Good Subarrays

Companies: Amazon, BNY Mellon, Harness, Microsoft

Array · Bit Manipulation · Monotonic Stack · Stack

Count Good Triplets in an Array

Count the number of value triplets (x,y,z) in two permutations of 0..n−1 such that the indices of x,y,z are strictly increasing in both arrays (they…

General practice

Count Hills and Valleys in an Array

Count how many hills and valleys appear in an array, where a position (or contiguous block of equal values) is a hill if its value…

General practice

Count Houses in a Circular Street II

Count the number of valid ways to choose or label houses arranged in a circle subject to local constraints (for example, restrictions on adjacent selections…

General practice

Count Increasing Quadruplets

Count the number of index quadruplets (i<j<k<l) in a permutation nums of 1..n such that nums[i] < nums[k] < nums[j] < nums[l]. With n up…

General practice

Count Indices With Opposite Parity

General practice

Count Integers Appearing in a Single Block

General practice

Count Integers in Intervals

Maintain a dynamic set of closed integer intervals that supports adding an interval (merging overlaps) and returning the total number of distinct integers covered by…

General practice

Count Integers With Even Digit Sum

Count how many positive integers ≤ num have an even sum of digits. With num ≤ 1000 this is easily solved by computing each number's…

General practice

Count Islands With Total Value Divisible by K

Count the number of 4-directionally connected components of positive cells (islands) whose sum of cell values is divisible by k. The core challenge is to…

General practice

Count Items Matching a Rule

Given a list of items where each item is [type, color, name] and a ruleKey (type/color/name) plus ruleValue, return how many items have the corresponding…

General practice

Count K-Reducible Numbers Less Than N

Count how many positive integers less than n (given as binary string s) reach 1 within at most k iterations of replacing a number by…

General practice

Count K-Subsequences of a String With Maximum Beauty

Find the k distinct characters whose counts f(c) in s maximize the sum (beauty), then count how many k-length subsequences (distinct index choices) realize that…

General practice

Count K-th Roots in a Range

Companies: Google, Meta

Binary Search · Math