284. Number of Islands

Given an m x n 2D grid of "1" (land) and "0" (water), return the number of islands.

An island is formed by connecting adjacent lands horizontally or vertically.

Examples

numIslands([
  ['1', '1', '0'],
  ['1', '0', '0'],
  ['0', '0', '1'],
]); // 2

numIslands([
  ['0', '0'],
  ['0', '0'],
]); // 0