Medium
Given an m x n
2D binary grid grid
which represents a 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'
.# @param {Character[][]} grid
# @return {Integer}
def num_islands(grid)
islands = 0
if grid && !grid.empty? && !grid[0].empty?
(0...grid.length).each do |i|
(0...grid[0].length).each do |j|
if grid[i][j] == '1'
dfs_islands(grid, i, j)
islands += 1
end
end
end
end
islands
end
private
def dfs_islands(grid, x, y)
return if x.negative? || grid.length <= x || y.negative? || grid[0].length <= y || grid[x][y] != '1'
grid[x][y] = 'x'
dfs_islands(grid, x + 1, y)
dfs_islands(grid, x - 1, y)
dfs_islands(grid, x, y + 1)
dfs_islands(grid, x, y - 1)
end