Introduction

In this blog post, we'll share the most commonly asked coding interview questions at Yandex. 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: Longest Subarray of 1's After Deleting One Element

Given a binary array nums, you should delete one element from it. Return the size of the longest non-empty subarray containing only 1's in the resulting array. Return 0 if there is no such subarray. Example 1: Input: nums = [1,1,0,1] Output: 3 Explanation: After deleting the number in position 2, [1,1,1] contains 3 numbers with value of 1's. Example 2: Input: nums = [0,1,1,1,0,1,1,0,1] Output: 5 Explanation: After deleting the number in position 4, [0,1,1,1,1,1,0,1] longest subarray with value of 1's is [1,1,1,1,1]. Example 3: Input: nums = [1,1,1] Output: 2 Explanation: You must delete one element. Constraints: 1 <= nums.length <= 105 nums[i] is either 0 or 1.

Topics: Array, Dynamic Programming, Sliding Window

Problem #2: Summary Ranges

You are given a sorted unique integer array nums. A range [a,b] is the set of all integers from a to b (inclusive). Return the smallest sorted list of ranges that cover all the numbers in the array exactly. That is, each element of nums is covered by exactly one of the ranges, and there is no integer x such that x is in one of the ranges but not in nums. Each range [a,b] in the list should be output as: "a->b" if a != b "a" if a == b Example 1: Input: nums = [0,1,2,4,5,7] Output: ["0->2","4->5","7"] Explanation: The ranges are: [0,2] --> "0->2" [4,5] --> "4->5" [7,7] --> "7" Example 2: Input: nums = [0,2,3,4,6,8,9] Output: ["0","2->4","6","8->9"] Explanation: The ranges are: [0,0] --> "0" [2,4] --> "2->4" [6,6] --> "6" [8,9] --> "8->9" Constraints: 0 <= nums.length <= 20 -231 <= nums[i] <= 231 - 1 All the values of nums are unique. nums is sorted in ascending order.

Topics: Array

Problem #3: String Compression

Given an array of characters chars, compress it using the following algorithm: Begin with an empty string s. For each group of consecutive repeating characters in chars: If the group's length is 1, append the character to s. Otherwise, append the character followed by the group's length. The compressed string s should not be returned separately, but instead, be stored in the input character array chars. Note that group lengths that are 10 or longer will be split into multiple characters in chars. After you are done modifying the input array, return the new length of the array. You must write an algorithm that uses only constant extra space. Example 1: Input: chars = ["a","a","b","b","c","c","c"] Output: Return 6, and the first 6 characters of the input array should be: ["a","2","b","2","c","3"] Explanation: The groups are "aa", "bb", and "ccc". This compresses to "a2b2c3". Example 2: Input: chars = ["a"] Output: Return 1, and the first character of the input array should be: ["a"] Explanation: The only group is "a", which remains uncompressed since it's a single character. Example 3: Input: chars = ["a","b","b","b","b","b","b","b","b","b","b","b","b"] Output: Return 4, and the first 4 characters of the input array should be: ["a","b","1","2"]. Explanation: The groups are "a" and "bbbbbbbbbbbb". This compresses to "ab12". Constraints: 1 <= chars.length <= 2000 chars[i] is a lowercase English letter, uppercase English letter, digit, or symbol.

Topics: Two Pointers, String

Problem #4: Find K Closest Elements

Given a sorted integer array arr, two integers k and x, return the k closest integers to x in the array. The result should also be sorted in ascending order. An integer a is closer to x than an integer b if: |a - x| < |b - x|, or |a - x| == |b - x| and a < b Example 1: Input: arr = [1,2,3,4,5], k = 4, x = 3 Output: [1,2,3,4] Example 2: Input: arr = [1,1,2,3,4,5], k = 4, x = -1 Output: [1,1,2,3] Constraints: 1 <= k <= arr.length 1 <= arr.length <= 104 arr is sorted in ascending order. -104 <= arr[i], x <= 104

Topics: Array, Two Pointers, Binary Search, Sliding Window, Sorting, Heap (Priority Queue)

Problem #6: Maximize Distance to Closest Person

You are given an array representing a row of seats where seats[i] = 1 represents a person sitting in the ith seat, and seats[i] = 0 represents that the ith seat is empty (0-indexed). There is at least one empty seat, and at least one person sitting. Alex wants to sit in the seat such that the distance between him and the closest person to him is maximized. Return that maximum distance to the closest person. Example 1: Input: seats = [1,0,0,0,1,0,1] Output: 2 Explanation: If Alex sits in the second open seat (i.e. seats[2]), then the closest person has distance 2. If Alex sits in any other open seat, the closest person has distance 1. Thus, the maximum distance to the closest person is 2. Example 2: Input: seats = [1,0,0,0] Output: 3 Explanation: If Alex sits in the last seat (i.e. seats[3]), the closest person is 3 seats away. This is the maximum distance possible, so the answer is 3. Example 3: Input: seats = [0,1] Output: 1 Constraints: 2 <= seats.length <= 2 * 104 seats[i] is 0 or 1. At least one seat is empty. At least one seat is occupied.

Topics: Array

Problem #8: Subarray Sum Equals K

Given an array of integers nums and an integer k, return the total number of subarrays whose sum equals to k. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1,1,1], k = 2 Output: 2 Example 2: Input: nums = [1,2,3], k = 3 Output: 2 Constraints: 1 <= nums.length <= 2 * 104 -1000 <= nums[i] <= 1000 -107 <= k <= 107

Topics: Array, Hash Table, Prefix Sum

Problem #9: Merge Intervals

Given an array of intervals where intervals[i] = [starti, endi], merge all overlapping intervals, and return an array of the non-overlapping intervals that cover all the intervals in the input. Example 1: Input: intervals = [[1,3],[2,6],[8,10],[15,18]] Output: [[1,6],[8,10],[15,18]] Explanation: Since intervals [1,3] and [2,6] overlap, merge them into [1,6]. Example 2: Input: intervals = [[1,4],[4,5]] Output: [[1,5]] Explanation: Intervals [1,4] and [4,5] are considered overlapping. Constraints: 1 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 104

Topics: Array, Sorting

Problem #10: Isomorphic Strings

Given two strings s and t, determine if they are isomorphic. Two strings s and t are isomorphic if the characters in s can be replaced to get t. All occurrences of a character must be replaced with another character while preserving the order of characters. No two characters may map to the same character, but a character may map to itself. Example 1: Input: s = "egg", t = "add" Output: true Explanation: The strings s and t can be made identical by: Mapping 'e' to 'a'. Mapping 'g' to 'd'. Example 2: Input: s = "foo", t = "bar" Output: false Explanation: The strings s and t can not be made identical as 'o' needs to be mapped to both 'a' and 'r'. Example 3: Input: s = "paper", t = "title" Output: true Constraints: 1 <= s.length <= 5 * 104 t.length == s.length s and t consist of any valid ascii character.

Topics: Hash Table, String