LeetCode 200: Number of islands

题目：

给定一个二维网格，在其中包含1和0的空间中计算陆地区域的数量。每个岛屿由被水完全包围，并且其内部由连通的陆地位点构成。该网格的所有边界都被视为水体。

Consider a 2D grid where each cell is marked as '1' for land or '0' for water; determine the total number of islands. An island is entirely surrounded by water, defined as a group of connected land cells that are adjacent either horizontally or vertically. The grid's borders are all considered to be surrounded by water.

示例 1:

    输入:
    11110
    11010
    11000
    00000
    
    输出: 1

示例 2:

    输入:
    11000
    11000
    00100
    00011
    
    输出: 3

解题思路：

首先弄清楚什么