思考题：看题解可以使用 UnionFind 来解决这个问题。可以思考一下，如何实现？
这道题与 0130-surrounded-regions.adoc 类似。
Given a 2d grid map of ’1'`s (land) and ’0'`s (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.
Example 1:
Input: 11110 11010 11000 00000 Output: 1
Example 2:
Input: 11000 11000 00100 00011 Output: 3
link:{sourcedir}/_0200_NumberOfIslands.java[role=include]