You are given a grid representing a battleship field, where ‘X’ marks the location of a part of a battleship and ‘.’ represents an empty sea cell. A battleship is either placed horizontally or vertically on the grid, with no adjacent battleships (there must be at least one empty cell between any two battleships). Your task is to count the number of distinct battleships on the grid.
You are given the root of a binary tree and an integer targetSum. Your task is to count the total number of paths in the tree where the sum of node values along the path equals targetSum. The path does not need to start or end at the root or a leaf, but it must go downwards (from parent to child nodes).
Design an algorithm to serialize and deserialize a binary search tree (BST). Serialization is converting the tree to a string format, while deserialization reconstructs the tree from this string. The goal is to ensure that the BST can be serialized to a compact string and can be accurately deserialized back into the original tree structure.
Given the root of a binary search tree (BST) with possible duplicates, return the mode(s) (i.e., the most frequently occurring element) in the tree. If there are multiple modes, return them in any order.
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.
