Introduction

In this blog post, we'll share the most commonly asked coding interview questions at Tinkoff. If you don't have months to study for your interviews, you can use AI tools like Chatmagic to generate solutions quickly and efficiently - helping you pass the interviews and get the job offer!

Problem #1: Find First and Last Position of Element in Sorted Array

Given an array of integers nums sorted in non-decreasing order, find the starting and ending position of a given target value. If target is not found in the array, return [-1, -1]. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [5,7,7,8,8,10], target = 8 Output: [3,4] Example 2: Input: nums = [5,7,7,8,8,10], target = 6 Output: [-1,-1] Example 3: Input: nums = [], target = 0 Output: [-1,-1] Constraints: 0 <= nums.length <= 105 -109 <= nums[i] <= 109 nums is a non-decreasing array. -109 <= target <= 109

Topics: Array, Binary Search

Problem #2: Form Smallest Number From Two Digit Arrays

Given two arrays of unique digits nums1 and nums2, return the smallest number that contains at least one digit from each array. Example 1: Input: nums1 = [4,1,3], nums2 = [5,7] Output: 15 Explanation: The number 15 contains the digit 1 from nums1 and the digit 5 from nums2. It can be proven that 15 is the smallest number we can have. Example 2: Input: nums1 = [3,5,2,6], nums2 = [3,1,7] Output: 3 Explanation: The number 3 contains the digit 3 which exists in both arrays. Constraints: 1 <= nums1.length, nums2.length <= 9 1 <= nums1[i], nums2[i] <= 9 All digits in each array are unique.

Topics: Array, Hash Table, Enumeration

Problem #3: Minimum Difference Between Highest and Lowest of K Scores

You are given a 0-indexed integer array nums, where nums[i] represents the score of the ith student. You are also given an integer k. Pick the scores of any k students from the array so that the difference between the highest and the lowest of the k scores is minimized. Return the minimum possible difference. Example 1: Input: nums = [90], k = 1 Output: 0 Explanation: There is one way to pick score(s) of one student: - [90]. The difference between the highest and lowest score is 90 - 90 = 0. The minimum possible difference is 0. Example 2: Input: nums = [9,4,1,7], k = 2 Output: 2 Explanation: There are six ways to pick score(s) of two students: - [9,4,1,7]. The difference between the highest and lowest score is 9 - 4 = 5. - [9,4,1,7]. The difference between the highest and lowest score is 9 - 1 = 8. - [9,4,1,7]. The difference between the highest and lowest score is 9 - 7 = 2. - [9,4,1,7]. The difference between the highest and lowest score is 4 - 1 = 3. - [9,4,1,7]. The difference between the highest and lowest score is 7 - 4 = 3. - [9,4,1,7]. The difference between the highest and lowest score is 7 - 1 = 6. The minimum possible difference is 2. Constraints: 1 <= k <= nums.length <= 1000 0 <= nums[i] <= 105

Topics: Array, Sliding Window, Sorting

Problem #4: Number of Islands

Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water), return the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water. Example 1: Input: grid = [ ["1","1","1","1","0"], ["1","1","0","1","0"], ["1","1","0","0","0"], ["0","0","0","0","0"] ] Output: 1 Example 2: Input: grid = [ ["1","1","0","0","0"], ["1","1","0","0","0"], ["0","0","1","0","0"], ["0","0","0","1","1"] ] Output: 3 Constraints: m == grid.length n == grid[i].length 1 <= m, n <= 300 grid[i][j] is '0' or '1'.

Topics: Array, Depth-First Search, Breadth-First Search, Union Find, Matrix

Problem #5: Two Sum

Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target. You may assume that each input would have exactly one solution, and you may not use the same element twice. You can return the answer in any order. Example 1: Input: nums = [2,7,11,15], target = 9 Output: [0,1] Explanation: Because nums[0] + nums[1] == 9, we return [0, 1]. Example 2: Input: nums = [3,2,4], target = 6 Output: [1,2] Example 3: Input: nums = [3,3], target = 6 Output: [0,1] Constraints: 2 <= nums.length <= 104 -109 <= nums[i] <= 109 -109 <= target <= 109 Only one valid answer exists. Follow-up: Can you come up with an algorithm that is less than O(n2) time complexity?

Topics: Array, Hash Table