Imagine you have a special keyboard with the following keys:
- A: Print one ‘A’ on the screen.
- Ctrl-A: Select the whole screen.
- Ctrl-C: Copy selection to buffer.
- Ctrl-V: Print buffer on screen appending it after what has already been printed.
Given an integer n, return the maximum number of ‘A’ you can print on the screen with at most n presses on the keys.
634. Find the Derangement of An Array
In combinatorial mathematics, a derangement is a permutation of the elements of a set, such that no element appears in its original position.
You are given an integer n. There is originally an array consisting of n integers from 1 to n in ascending order, return the number of derangements it can generate. Since the answer may be huge, return it modulo 109 + 7.
Given a positive integer n, generate an n x n matrix filled with elements from 1 to n2 in spiral order.
2223. Sum of Scores of Built Strings
You are building a string s of length n one character at a time, prepending each new character to the front of the string. The strings are labeled from 1 to n, where the string with length i is labeled si.
- For example, for s = “abaca”, s1 == “a”, s2 == “ca”, s3 == “aca”, etc.
The score of si is the length of the longest common prefix between si and sn (Note that s == sn).
Given the final string s, return the sum of the score of every si.
2220. Minimum Bit Flips to Convert Number
A bit flip of a number x is choosing a bit in the binary representation of x and flipping it from either 0 to 1 or 1 to 0.
- For example, for x = 7, the binary representation is 111 and we may choose any bit (including any leading zeros not shown) and flip it. We can flip the first bit from the right to get 110, flip the second bit from the right to get 101, flip the fifth bit from the right (a leading zero) to get 10111, etc.
Given two integers start and goal, return the minimum number of bit flips to convert start to goal.
2221. Find Triangular Sum of an Array
You are given a 0-indexed integer array nums, where nums[i] is a digit between 0 and 9 (inclusive).
The triangular sum of nums is the value of the only element present in nums after the following process terminates:
- Let nums comprise of n elements. If n == 1, end the process. Otherwise, create a new 0-indexed integer array newNums of length n - 1.
- For each index i, where 0 <= i < n - 1, assign the value of newNums[i] as (nums[i] + nums[i+1]) % 10, where % denotes modulo operator.
- Replace the array nums with newNums.
- Repeat the entire process starting from step 1.
Return the triangular sum of nums.
2222. Number of Ways to Select Buildings
You are given a 0-indexed binary string s which represents the types of buildings along a street where:
- s[i] = ‘0’ denotes that the ith building is an office and
- s[i] = ‘1’ denotes that the ith building is a restaurant.
As a city official, you would like to select 3 buildings for random inspection. However, to ensure variety, no two consecutive buildings out of the selected buildings can be of the same type.
- For example, given s = “001101”, we cannot select the 1st, 3rd, and 5th buildings as that would form “011” which is not allowed due to having two consecutive buildings of the same type.
Return the number of valid ways to select 3 buildings.
There is a 2D grid of size n x n where each cell of this grid has a lamp that is initially turned off.
You are given a 2D array of lamp positions lamps, where lamps[i] = [rowi, coli] indicates that the lamp at grid[rowi][coli] is turned on. Even if the same lamp is listed more than once, it is turned on.
When a lamp is turned on, it illuminates its cell and all other cells in the same row, column, or diagonal.
You are also given another 2D array queries, where queries[j] = [rowj, colj]. For the jth query, determine whether grid[rowj][colj] is illuminated or not. After answering the jth query, turn off the lamp at grid[rowj][colj] and its 8 adjacent lamps if they exist. A lamp is adjacent if its cell shares either a side or corner with grid[rowj][colj].
Return an array of integers ans, where ans[j] should be 1 if the cell in the jth query was illuminated, or 0 if the lamp was not.
1557. Minimum Number of Vertices to Reach All Nodes
Given a directed acyclic graph, with n vertices numbered from 0 to n-1, and an array edges where edges[i] = [fromi, toi] represents a directed edge from node fromi to node toi.
Find the smallest set of vertices from which all nodes in the graph are reachable. It’s guaranteed that a unique solution exists.
Notice that you can return the vertices in any order.
750. Number Of Corner Rectangles
Given an m x n integer matrix grid where each entry is only 0 or 1, return the number of corner rectangles.
A corner rectangle is four distinct 1’s on the grid that forms an axis-aligned rectangle. Note that only the corners need to have the value 1. Also, all four 1’s used must be distinct.