Counting Islands

Problem

Given a 2D grid grid of 1s (land) and 0s (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 surrounded by water.

Examples

numIslands([
  [1, 1, 0],
  [1, 0, 0],
  [0, 1, 1]
]) 
// returns 2
/* 
There are two islands in the grid. 
The first island is at [(0,0), (0,1), (1,0)].
The second island is at [(2,1), (2,2)].
*/