Given an integer array arr and an integer difference, find the length of the longest subsequence in arr such that the difference between each adjacent element in the subsequence equals the given difference.
In a gold mine grid of size m x n, each cell contains an integer representing the amount of gold in that cell. A cell with 0 means no gold is present. The task is to find the maximum amount of gold that can be collected by following certain movement rules: You can move one step in any of the four directions (left, right, up, down), but you cannot visit the same cell twice, and you cannot move to a cell that contains 0 gold.
On an 8x8 chessboard, there are multiple black queens and one white king. You are given the positions of the black queens and the white king. Your task is to find all the black queens that can directly attack the white king. A queen can attack the king if they share the same row, column, or diagonal.
You are given an array of coordinates, where each coordinate represents a point in the 2D plane. Your task is to check if all the points in the array lie on the same straight line.
You are given a list of folder paths, where each path represents a folder in the file system. The task is to remove all sub-folders from the list, keeping only the main folders.
You are given an array of strings arr. Return the maximum possible length of a string s formed by concatenating a subsequence of arr such that all characters in s are unique.