Introduction

In this blog post, we'll share the most commonly asked coding interview questions at HP. 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: Minimum Recolors to Get K Consecutive Black Blocks

You are given a 0-indexed string blocks of length n, where blocks[i] is either 'W' or 'B', representing the color of the ith block. The characters 'W' and 'B' denote the colors white and black, respectively. You are also given an integer k, which is the desired number of consecutive black blocks. In one operation, you can recolor a white block such that it becomes a black block. Return the minimum number of operations needed such that there is at least one occurrence of k consecutive black blocks. Example 1: Input: blocks = "WBBWWBBWBW", k = 7 Output: 3 Explanation: One way to achieve 7 consecutive black blocks is to recolor the 0th, 3rd, and 4th blocks so that blocks = "BBBBBBBWBW". It can be shown that there is no way to achieve 7 consecutive black blocks in less than 3 operations. Therefore, we return 3. Example 2: Input: blocks = "WBWBBBW", k = 2 Output: 0 Explanation: No changes need to be made, since 2 consecutive black blocks already exist. Therefore, we return 0. Constraints: n == blocks.length 1 <= n <= 100 blocks[i] is either 'W' or 'B'. 1 <= k <= n

Topics: String, Sliding Window

Problem #2: Minimum Cost Homecoming of a Robot in a Grid

There is an m x n grid, where (0, 0) is the top-left cell and (m - 1, n - 1) is the bottom-right cell. You are given an integer array startPos where startPos = [startrow, startcol] indicates that initially, a robot is at the cell (startrow, startcol). You are also given an integer array homePos where homePos = [homerow, homecol] indicates that its home is at the cell (homerow, homecol). The robot needs to go to its home. It can move one cell in four directions: left, right, up, or down, and it can not move outside the boundary. Every move incurs some cost. You are further given two 0-indexed integer arrays: rowCosts of length m and colCosts of length n. If the robot moves up or down into a cell whose row is r, then this move costs rowCosts[r]. If the robot moves left or right into a cell whose column is c, then this move costs colCosts[c]. Return the minimum total cost for this robot to return home. Example 1: Input: startPos = [1, 0], homePos = [2, 3], rowCosts = [5, 4, 3], colCosts = [8, 2, 6, 7] Output: 18 Explanation: One optimal path is that: Starting from (1, 0) -> It goes down to (2, 0). This move costs rowCosts[2] = 3. -> It goes right to (2, 1). This move costs colCosts[1] = 2. -> It goes right to (2, 2). This move costs colCosts[2] = 6. -> It goes right to (2, 3). This move costs colCosts[3] = 7. The total cost is 3 + 2 + 6 + 7 = 18 Example 2: Input: startPos = [0, 0], homePos = [0, 0], rowCosts = [5], colCosts = [26] Output: 0 Explanation: The robot is already at its home. Since no moves occur, the total cost is 0. Constraints: m == rowCosts.length n == colCosts.length 1 <= m, n <= 105 0 <= rowCosts[r], colCosts[c] <= 104 startPos.length == 2 homePos.length == 2 0 <= startrow, homerow < m 0 <= startcol, homecol < n

Topics: Array, Greedy

Problem #3: Longest Palindrome

Given a string s which consists of lowercase or uppercase letters, return the length of the longest palindrome that can be built with those letters. Letters are case sensitive, for example, "Aa" is not considered a palindrome. Example 1: Input: s = "abccccdd" Output: 7 Explanation: One longest palindrome that can be built is "dccaccd", whose length is 7. Example 2: Input: s = "a" Output: 1 Explanation: The longest palindrome that can be built is "a", whose length is 1. Constraints: 1 <= s.length <= 2000 s consists of lowercase and/or uppercase English letters only.

Topics: Hash Table, String, Greedy