Time:O(mn) Space:O(1) C++ class Solution { public: int countBattleships(vector<vector<char>>& board) { int ans = 0; for (int i = 0; i < board.size(); ++i) for (int j = 0; j < board[0].size(); ++j) { if (board[i][j] == '.') continue; if (i > 0 && board[i - 1][j] == 'X') continue; if (j > 0 && board[i][j - 1] == 'X') continue; ++ans; } return ans; } }; JAVA class Solution { public int countBattleships(char[][] board) { int ans = 0; for (int i = 0; i < board.length; ++i) for (int j = 0; j < board[0].length; ++j) { if (board[i][j] == '.') continue; if (i > 0 && board[i - 1][j] == 'X') continue; if (j > 0 && board[i][j - 1] == 'X') continue; ++ans; } return ans; } }