A magical string consists of only ‘1’ and ‘2’ and follows a special rule: the number of consecutive occurrences of characters ‘1’ and ‘2’ generates the string itself. Given an integer n, return the number of ‘1’s in the first n characters of the magical string.
You are given an integer array nums. Two players, Player 1 and Player 2, take turns to pick numbers from either end of the array. Each player adds the selected number to their score. The goal is to determine if Player 1 can win the game. Player 1 wins if they have a higher score or if the scores are tied.
You are given an integer array nums and an integer target. You must build an expression by adding ‘+’ or ‘-’ before each element in nums and concatenate them to form an expression. Return the number of different expressions that result in the target value.
You are given an array of non-overlapping axis-aligned rectangles. Each rectangle is represented by its bottom-left and top-right corner. Your task is to design a system that can pick a random integer point from the space covered by one of the given rectangles. A point on the perimeter of a rectangle is considered inside the rectangle.
You are given an m x n matrix. The task is to return an array that contains all the elements of the matrix in diagonal order, starting from the top-left and moving diagonally towards the bottom-right. The diagonal order alternates between upward and downward diagonals.
Given the root of a binary tree, return the most frequent subtree sum. A subtree sum is the sum of all the node values in the subtree rooted at any node, including the node itself. If there is a tie, return all the subtree sums with the highest frequency.
