Od problemu do algorytmu

Answer the introductory questions:

1. What is an algorithmalgorithmalgorithm?

2. Provide a recipereciperecipe for boiling water in an electric kettle?

3. Will the recipe for boiling water in the kettle on the stove look the same?

4. Suggest a recipe for boiling water describing both cases.

Certainly you have already realized that electronic devices, including computers, tablets or smartphones, work strictly according to the „recipes” developed by people. However, before the programmerprogrammerprogrammer enters the codecodecode into the memory of such a machine, on the basis of which it will perform the tasks assigned to it, it is necessary to carefully analyse what the device should do and in what situation. Seemingly, it seems to be simple, but when we start to create such a recipereciperecipe, which is technically called an algorithmalgorithmalgorithm, it turns out that it is complicated and many situations have to be anticipated.

Let's try to create an algorithm for ... an elevator - a device we often use.

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Zdjęcie przedstawia przyciski w windzie, rozmieszczone w dwóch kolumnach po trzy. Środkowe przyciski są nieopisane. W lewej kolumnie od góry cyfra zero, na dole ikona dzwonka. W prawej kolumnie od góry cyfra jeden, na dole ikona otwierania drzwi (trójkąt skierowany wierzchołkiem w lewą stronę, prostokąt, trójkąt skierowany wierzchołkiem w prawą stronę).

Imagine that the elevator runs only between two floors:

• ground floor level,

• first floor level.

Our algorithm in the simplest case will be based on the following commands:

• go up,

• go down,

• stop the elevator,

• open the door,

• close the door.

And information:

• the call button was pressed on the ground floor,

• the call button was pressed on the first floor,

• the 'to the ground floor' selection button was pressed in the elevator,

• the 'to the first floor' selection button was pressed in the elevator.

And the variablevariablevariable 'storey', which will take the valuevaluevalue 'ground floor' if the elevator will be located on the ground floor or 'first floor' when it is on the first floor.

The simplest algorithmalgorithmalgorithm that would cause a passenger who approaches the elevator on the ground floor to go up, would look like this:

• if 'the call button was pressed on the ground floor' - open the door,

• if the 'to the first floor' selection button was pressed in the elevator - close the door,

• go up,

• if level equals 'first floor' - stop the elevator,

• open the door.

The algorithm is very simple, but we actually assumed that the elevator is downstairs waiting for the passenger, so that does not have to be true.

So it's time for you.

When you deal with the above tasks, think that the real elevator still:

• reacts to the 'stop' emergency button,

• takes passengers on the way from other storeys if they pressed the call button in the direction in which the elevator moves ('up or down'),

• will not stop 'on the way' if there is already a maximum number of passengers in the elevator.

The commands used by you in the algorithms are written using the graphic symbols shown in the interactive picture.

An algorithmalgorithmalgorithm is a procedure that ultimately leads to a specific effect. The algorithm should be correct, finite, effective, unambiguous and universal. It means that it should cover all possible cases describing a given situation. In the end it should always give the correct result after completing the finite number of actions.

Exercises

Glossary

Keywords

algorithmalgorithmalgorithm

codecodecode

instructioninstructioninstruction

programmerprogrammerprogrammer

recipereciperecipe