zoukankan      html  css  js  c++  java
  • 419. 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:

    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?

     FOLLOW UP

        //little tricky way only care about the left and up case
        public int countBattleships(char[][] board) {
           if(board == null || board.length == 0) return 0;
           int row = board.length;
           int col = board[0].length;
           int res = 0;
           for(int i = 0; i < row ; i++){
               for(int j = 0; j < col ; j++){
                   if(board[i][j] == 'X'){
                       if(i > 0 && board[i-1][j] == 'X') continue;
                       if(j > 0 && board[i][j-1] == 'X') continue;
                       res++;
                   }
               }
           }
           return res;
        
        }

    DFS

    public class Solution {
        public int countBattleships(char[][] board) {
           if(board == null || board.length == 0) return 0;
           int row = board.length;
           int col = board[0].length;
           int res = 0;
           for(int i = 0; i < row ; i++){
               for(int j = 0; j < col ; j++){
                   if(board[i][j] == 'X'){
                       dfs(board , i, j);
                       res++;
                   }
               }
           }
           return res;
        }
        public void dfs(char[][] board, int i, int j){
            if(i < 0 || i >= board.length || j < 0 || j >=board[0].length || board[i][j] == '.'){
                return;
            }
            board[i][j] = '.';
            dfs(board , i+1, j);
            dfs(board , i, j+1);
            dfs(board , i-1, j);
            dfs(board , i, j-1);
        }
    }
  • 相关阅读:
    jquery实现全选、不选、反选的两种方法
    EasyGui
    PyInstaller打包成exe可执行文件
    paramiko模块
    仿照admin写一个startk组件
    django-model之Q查询补充
    django-Model _meta API
    django-admin的源码流程
    权限管理具体代码实现
    021.15 IO流 其他流
  • 原文地址:https://www.cnblogs.com/joannacode/p/6108135.html
Copyright © 2011-2022 走看看