Number of Islands

package main

import "fmt"

func numIslands(grid [][]byte) int {
	rows, cols := len(grid), len(grid[0])
	count := 0

	var sink func(int, int)
	sink = func(r, c int) {
		if r < 0 || r >= rows || c < 0 || c >= cols || grid[r][c] != '1' {
			return
		}
		grid[r][c] = '0'
		sink(r+1, c)
		sink(r-1, c)
		sink(r, c+1)
		sink(r, c-1)
	}

	for r := 0; r < rows; r++ {
		for c := 0; c < cols; c++ {
			if grid[r][c] == '1' {
				count++
				sink(r, c)
			}
		}
	}
	return count
}

func main() {
	grid := [][]byte{
		{'1', '1', '0', '0', '0'},
		{'1', '1', '0', '0', '0'},
		{'0', '0', '1', '0', '0'},
		{'0', '0', '0', '1', '1'},
	}
	fmt.Println(numIslands(grid)) // 3
}