README.md

419. Battleships in a Board

Given an 2D board, count how many 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.

Example:

X..X
...X
...X

In the above board there are 2 battleships.

Invalid Example:

...X
XXXX
...X

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

Follow up:

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

Solutions (Rust)

1. Solution

impl Solution {
    pub fn count_battleships(board: Vec<Vec<char>>) -> i32 {
        let mut ret = 0;

        for i in 0..board.len() {
            for j in 0..board[0].len() {
                if board[i][j] == 'X' &&
                (i + 1 == board.len() || board[i + 1][j] == '.') &&
                (j + 1 == board[0].len() || board[i][j + 1] != 'X') {
                    ret += 1;
                }
            }
        }

        ret
    }
}