题目：

题解：

func numIslands(grid [][]byte) int {res := 0for i := 0; i < len(grid); i++ {for j := 0; j < len(grid[i]); j++ {if grid[i][j] == '1' {res++dfs(grid, i, j)}}}return res
}func dfs(grid [][]byte, r, c int) {h, w := len(grid), len(grid[0])if r < 0 || r >= h || c < 0 || c >= w {return}if grid[r][c] == '0' {return}grid[r][c] = '0'dfs(grid, r-1, c)dfs(grid, r+1, c)dfs(grid, r, c-1)dfs(grid, r, c+1)
}