Number of Islands

def num_islands(grid)
  return 0 if not grid
  result = 0
  grid.length.times do |i|
    grid[0].length.times do |j|
      if grid[i][j] == 1
        result += 1
        extend(grid,i,j)
      end
    end
  end
  result
end

def extend(grid,i,j)
  if i < grid.length and j < grid[0].length and i >= 0 and j >= 0 and grid[i][j] == 1
    grid[i][j] = 0
    extend(grid,i+1,j)
    extend(grid,i,j+1)
    extend(grid,i-1,j)
    extend(grid,i,j-1)
    extend(grid,i-1,j-1)
    extend(grid,i-1,j+1)
    extend(grid,i+1,j-1)
    extend(grid,i+1,j+1)
  end
end

grid = [
  [1,1,0,0,0],
  [0,1,0,0,1],
  [1,0,0,1,1],
  [0,0,0,0,0],
  [1,0,1,0,1] ]

print num_islands(grid)