Pour water on a landscape

2015-07-08

Description of the problem

Rain is pouring for a defined duration on a landscape that consists of multiple columns, each with its own height.

Rules

There is an invisible border to the left and to the right of the provided landscape with a height of infinity.
Each hour of rain pours one unit of rain into each column.
The rain flows from a higher to a lower column. If the column to the left and to the right are both lower, then the rain distributes evenly between those two.

At first glance it might seem logical to start pouring the rain from above one hour at a time and distribute it like that.
But if the landscape is slowly filled from the bottom up, many many edge cases will never occur and the problem will be a lot easier to implement.

2. Create regions

Instead of working with each column, I chose to group columns of the same height together into a region.
This will reduce the number of elements that need checking and allows me to easily calculate the water capacity of a region and also if the water should flow somewhere from this element.

3. Gather the rain in the trenches/ local minima

If the landscape will get bigger, it will be very inefficient to pour the water into each column.
Instead it would be easier to find all local minima in the landscape and divide the rain among those minima in the beginning.
This of course costs some time in the beginning of the calculation, especially if the worst case should occur: A zigzag landscape.

4. Shortcut if a landscape overflows

I can skip a lot of calculation if I add a case that checks in the beginning if more water will be poured into the landscape than it can take.

Code

The code for solving this problem is split into two files: region.js and solver.js.

region.js contains the prototype for each Region instance with the necessary functions to pour rain into itself or another region and merge it with neighbors to create a bigger region. Also it contains the specific border, a region with a height of POSITIVE_INFINITY.
solver.js contains the code to create the double-linked list of regions from the entered landscape array, and to pour all the rain into the landscape.

Host a wifi hotspot on Windows 8

2015-03-14

If no Wifi, usb pen drive or network cable is available, it is sometimes useful to start a private Wifi hotspot on your computer.

This is achievable using the netsh tool.

Note: Usually a network card can be either used for receiving or sending a Wifi signal. Connecting to a wireless network and hosting another one at the same time is not possible.

Check if hosting a network is supported by the driver

If you execute the command

netsh wlan show drivers

on the command line, the response should contain the line

...
Hosted network supported  : Yes
...

If it does not, you are out of luck

Register a network

netsh wlan set hostednetwork mode=allow ssid=Horst key=111222333

register.bat

You can omit the key, but you should definitely add a password (even a short one).

Using the created network

To verify the status of the network

netsh wlan show hostednetwork

show_info.bat

To start the network

netsh wlan show hostednetwork

To stop the network

netsh wlan show hostednetwork

For convenience I added both starting and stopping to one batch script.
After a keypress, the wifi network is stopped again.

@ECHO OFF

netsh wlan start hostednetwork

PAUSE

netsh wlan stop hostednetwork

start_and_stop.bat

Thesis: WebRTC multipoint conferencing

2015-02-28

with recording using a Media Server

My thesis is done, unfortunately I cannot share any of the code, but the presentation and the thesis itself are mine to distribute.

The presentation

presentation cover — I do not own any of the pictures, please see the sources section

The thesis

Abstract

Goal is to both research and implement a multipoint communication solution that uses WebRTC for audio and video transmission. The conference size should be arbitrary but support at least four participants and allow multiple conferences at the same time. The solution should contain recording functionality and allow participation of devices in restrictive network environments.

These goals were met by using a a media server that allows to significantly increase the conference size from the maximum of four when using a full mesh peer-to-peer architecture.

This thesis is separated into two parts: The first consists of an introduction to WebRTC, research and theoretical assumptions that lead to an implementation strategy. The second part contains information about the selected media server, follows the implementation of the prototype solution and describes parts of its architecture.

The prototype itself is not part of this thesis.

Included are benchmark results for WebRTC conferences concerning the bandwidth requirements for different multipoint architecture patterns and screen resolutions. Those were conducted using the prototype application.