200. Number of Islands

Given an m x n 2d grid map of '1's (land) and '0's (water), return 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: grid = [
  ["1","1","1","1","0"],
  ["1","1","0","1","0"],
  ["1","1","0","0","0"],
  ["0","0","0","0","0"]
]
Output: 1

Example 2:

Input: grid = [
  ["1","1","0","0","0"],
  ["1","1","0","0","0"],
  ["0","0","1","0","0"],
  ["0","0","0","1","1"]
]
Output: 3

Constraints:

• m == grid.length
• n == grid[i].length
• 1 <= m, n <= 300
• grid[i][j] is '0' or '1'.

# @lc code=start
using LeetCode

function lands_num(grid::Vector{Vector{String}})
    nr, nc = length(grid), length(grid[1])
    function dfs(grid::Vector{Vector{String}}, r, c)
        grid[r][c] = "0"
        (r + 1 <= nr) && grid[r+1][c] == "1" && dfs(grid, r+1, c)
        (r - 1 > 0) && grid[r-1][c] == "1" && dfs(grid, r-1, c)
        (c + 1 <= nc) && grid[r][c+1] == "1" && dfs(grid, r, c+1)
        (c - 1 > 0) && grid[r][c-1] == "1" && dfs(grid, r, c-1)
        nothing
    end
    res = 0
    for i in 1:nr
        for j in 1:nc
            if grid[i][j] == "1"
                res += 1
                dfs(grid, i, j)
            end
        end
    end
    res
end
# @lc code=end

lands_num (generic function with 1 method)

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