solution.go

package main

import "fmt"

func numIslands(grid [][]byte) int {
	if grid == nil || len(grid) == 0 {
		return 0
	}

	result := 0
	for i := 0; i < len(grid); i++ {
		for j := 0; j < len(grid[i]); j++ {
			if grid[i][j] == '1' {
				result += dfs(grid, i, j)
			}
		}
	}
	return result
}

func dfs(grid [][]byte, i int, j int) int {
	if i < 0 || i >= len(grid) || j < 0 || j >= len(grid[i]) || grid[i][j] == '0' {
		return 0
	}
	grid[i][j] = '0'
	dfs(grid, i+1, j)
	dfs(grid, i-1, j)
	dfs(grid, i, j+1)
	dfs(grid, i, j-1)
	return 1
}

func main() {
	grid1 := [][]byte{
		{'1', '1', '1', '1', '0'},
		{'1', '1', '0', '1', '0'},
		{'1', '1', '0', '0', '0'},
		{'0', '0', '0', '0', '0'},
	}
	grid2 := [][]byte{
		{'1', '1', '0', '0', '0'},
		{'1', '1', '0', '0', '0'},
		{'0', '0', '1', '0', '0'},
		{'0', '0', '0', '1', '1'},
	}
	fmt.Println(numIslands(grid1))
	fmt.Println(numIslands(grid2))
}