200. Number of Islands.

Code

from typing import List

def numIslands(grid:List[List[str]]) -> int:
  def dfs(i, j):
    # 더 이상 땅이 아닌 경우 종료
    if i < 0 or i >= len(grid) or j < 0 or j >= len(grid[0]) or grid[i][j] != '1':
      return

    grid[i][j] = 0
    dfs(i + 1, j)
    dfs(i - 1 , j)
    dfs(i, j + 1)
    dfs(i, j -1)

  count = 0
  for i in range(len(grid)):
    for j in range(len(grid[0])):
      if grid[i][j] == '1':
        dfs(i, j)
        # 모든 육지 탐색 후 +1
        count += 1
  return count