419. Battleships in a Board

  • 60.6%

https://leetcode.com/problems/battleships-in-a-board/

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.
    Example:
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> X..X
> ...X
> ...X
>

In the above board there are 2 battleships.
Invalid Example:

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> ...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?

java

4ms, October 18, 2016

https://discuss.leetcode.com/topic/62970/simple-java-solution

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public class Solution {
public int countBattleships(char[][] board) {
int m = board.length;
if(m==0) return 0;
int n = board[0].length;

int count = 0;

for(int i=0; i<m; i++)
for(int j=0; j<n; j++){
if(board[i][j] == '.') continue;
if(i>0 && board[i-1][j] == 'X') continue;
if(j>0 && board[i][j-1] == 'X') continue;
count++;
}

return count;
}
}
谢谢你,可爱的朋友。