Battleships in a board

Array Depth-First Search Matrix

77.4% acceptance

Jan 13, 2026

2506

1026

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).

Solution

Rust

Time O(n²)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn count_battleships(board: Vec<Vec<char>>) -> i32 {
    let mut count = 0;
    for i in 0..board.len() {
      for j in 0..board[0].len() {
        if board[i][j] == 'X' {
          if (i == 0 || board[i - 1][j] == '.') && (j == 0 || board[i][j - 1] == '.') {
            count += 1;
          }
        }
      }
    }
    count
  }
}