number_of_islands.go

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

	cols := len(grid)
	rows := len(grid[0])
	var islands int

	var visit func(col, row int)
	visit = func(col, row int) {
		if col < 0 || col >= cols {
			return
		}
		if row < 0 || row >= rows {
			return
		}
		if grid[col][row] != '1' {
			return
		}

		grid[col][row] = '2'

		visit(col+1, row)
		visit(col, row+1)
		visit(col-1, row)
		visit(col, row-1)
	}

	for col := 0; col < cols; col++ {
		for row := 0; row < rows; row++ {
			if grid[col][row] == '1' {
				islands++
				visit(col, row)
			}

		}
	}

	return islands
}