1706. Where Will the Ball Fall

You have a 2-D grid of size m x n representing a box, and you have n balls. The box is open on the top and bottom sides.

Each cell in the box has a diagonal board spanning two corners of the cell that can redirect a ball to the right or to the left.

• A board that redirects the ball to the right spans the top-left corner to the bottom-right corner and is represented in the grid as 1.
• A board that redirects the ball to the left spans the top-right corner to the bottom-left corner and is represented in the grid as -1.

We drop one ball at the top of each column of the box. Each ball can get stuck in the box or fall out of the bottom. A ball gets stuck if it hits a “V” shaped pattern between two boards or if a board redirects the ball into either wall of the box.

Return an array answer of size n where answer[i] is the column that the ball falls out of at the bottom after dropping the ball from the ith column at the top, or -1 if the ball gets stuck in the box.

1554. Strings Differ by One Character

Given a list of strings dict where all the strings are of the same length.

Return true if there are 2 strings that only differ by 1 character in the same index, otherwise return false.

286. Walls and Gates

You are given an m x n grid rooms initialized with these three possible values.

• -1 A wall or an obstacle.
• 0 A gate.
• INF Infinity means an empty room. We use the value 231 - 1 = 2147483647 to represent INF as you may assume that the distance to a gate is less than 2147483647.

Fill each empty room with the distance to its nearest gate. If it is impossible to reach a gate, it should be filled with INF.

676. Implement Magic Dictionary

Design a data structure that is initialized with a list of different words. Provided a string, you should determine if you can change exactly one character in this string to match any word in the data structure.

Implement the MagicDictionary class:

• MagicDictionary() Initializes the object.
• void buildDict(String[] dictionary) Sets the data structure with an array of distinct strings dictionary.
• bool search(String searchWord) Returns true if you can change exactly one character in searchWord to match any string in the data structure, otherwise returns false.

379. Design Phone Directory

Design a phone directory that initially has maxNumbers empty slots that can store numbers. The directory should store numbers, check if a certain slot is empty or not, and empty a given slot.

Implement the PhoneDirectory class:

• PhoneDirectory(int maxNumbers) Initializes the phone directory with the number of available slots maxNumbers.
• int get() Provides a number that is not assigned to anyone. Returns -1 if no number is available.
• bool check(int number) Returns true if the slot number is available and false otherwise.
• void release(int number) Recycles or releases the slot number.

249. Group Shifted Strings

We can shift a string by shifting each of its letters to its successive letter.

• For example, “abc” can be shifted to be “bcd”.
  We can keep shifting the string to form a sequence.

• For example, we can keep shifting “abc” to form the sequence: “abc” -> “bcd” -> … -> “xyz”.

Given an array of strings strings, group all strings[i] that belong to the same shifting sequence. You may return the answer in any order.

447. Number of Boomerangs

You are given n points in the plane that are all distinct, where points[i] = [xi, yi]. A boomerang is a tuple of points (i, j, k) such that the distance between i and j equals the distance between i and k (the order of the tuple matters).

Return the number of boomerangs.

2183. Count Array Pairs Divisible by K

Given a 0-indexed integer array nums of length n and an integer k, return the number of pairs (i, j) such that:

• 0 <= i < j <= n - 1 and
• nums[i] * nums[j] is divisible by k.

2180. Count Integers With Even Digit Sum

Given a positive integer num, return the number of positive integers less than or equal to num whose digit sums are even.

The digit sum of a positive integer is the sum of all its digits.

2181. Merge Nodes in Between Zeros

You are given the head of a linked list, which contains a series of integers separated by 0’s. The beginning and end of the linked list will have Node.val == 0.

For every two consecutive 0’s, merge all the nodes lying in between them into a single node whose value is the sum of all the merged nodes. The modified list should not contain any 0’s.

Return the head of the modified linked list.