# LeetCode419 Battleships in a Board

## 描述

Given an 2D board, count how many different battleships are in it. The battleships are represented with 'X's, empty slots are represented with '.'s. You may assume the following rules:

• You receive a valid board, made of only battleships or empty slots.
• Battleships can only be placed horizontally or vertically. In other words, they can only be made of the shape 1xN (1 row, N columns) or Nx1 (N rows, 1 column), where N can be of any size.
• At least one horizontal or vertical cell separates between two battleships - there are no adjacent battleships.

## 样例

In the above board there are 2 battleships.

Invalid Example:

This is an invalid board that you will not receive - as battleships will always have a cell separating between them.

Could you do it in one-pass, using only O(1) extra memory and without modifying the value of the board?

DFS版：