Given an m x n matrix board where each cell is a battleship ‘X’ or empty ‘.’, return the number of the battleships on board. Battleships can only be placed horizontally or vertically on board. In othe

Given a string array words, return an array of all characters that show up in all strings within the words (including duplicates). You may return the answer in any order. Example 1:Input: words =

You are given an 8 x 8 matrix representing a chessboard. There is exactly one white rook represented by ‘R’, some number of white bishops ‘B’, and some number of black pawns ‘p’. Empty squares are rep

Given two integers left and right that represent the range [left, right], return the bitwise AND of all numbers in this range, inclusive. Example 1:Input: left = 5, right = 7Output: 4 Exampl

Given an input string, reverse the string word by word. Example 1:Input: “the sky is blue”Output: “blue is sky the” Example 2:Input: “ hello world! “Output: “world! hello”Explanation: Your reversed st

There is a robot on an m x n grid. The robot is initially located at the top-left corner (i.e., grid[0][0]). The robot tries to move to the bottom-right corner (i.e., grid[m - 1][n - 1]). The robot ca

Given a non-empty, singly linked list with head node head, return a middle node of linked list. If there are two middle nodes, return the second middle node. Example 1:Input: [1,2,3,4,5]Output: Node 3

Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. Return the answer in any order. A mapping of digits to letters (just like

You are given the root of a binary tree containing digits from 0 to 9 only. Each root-to-leaf path in the tree represents a number. For example, the root-to-leaf path 1 -> 2 -> 3 represents the

Given the root of a complete binary tree, return the number of the nodes in the tree. According to Wikipedia, every level, except possibly the last, is completely filled in a complete binary tree, and