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 other words, they can only be made of the shape 1 x k ( 1 row, k columns) or k x 1 ( k rows, 1 column), where k can be of any size. At least one horizontal or vertical cell separates between two battleships (i.e., there are no adjacent battleships).
m == board.lengthn == board[i].length1 <= m, n <= 200board[i][j] is either '.' or 'X' .Follow up: Could you do it in one-pass, using only O(1) extra memory and without modifying the values board ?