psynosaur / _marsrover

This was built to solve a challenge sent for an technical assessment

Mars Rover challenge

These are my observations and notes, they are not in any particulare order, however the code is structured in such a way that these observations make more sense.

Built using .Net Core 3.1 CLI application template from JetBrains Rider 2020.3

For completeness sake : https://code.google.com/archive/p/marsrovertechchallenge/

These are my assumptions and notes on the problem which I will turn into code.

• This plateau, which is curiously rectangular, must be navigated by the rovers so that their on board cameras can get a complete view of the surrounding terrain to send back to Earth.
• A rover's position is represented by a combination of an x and y co-ordinates and a letter representing one of the four cardinal compass points.
• The plateau is divided up into a grid to simplify navigation.
  • An example position might be 0, 0, N, which means the rover is in the bottom left corner and facing North.
• In order to control a rover, NASA sends a simple string of letters.
  • The possible letters are 'L', 'R' and 'M'.
  • This defines "turning" the rover
    • 'L' and 'R' makes the rover spin 90 degrees left or right respectively, without moving from its current spot.
  • This defines "moving" the rover
    • 'M' means move forward one grid point, and maintain the same heading.
• Assume that the square/coordinate directly North from (x, y) is (x, y+1).
  • THIS IS IMPORTANT !!
  • It defines what a rover does when moving up N
    • Northern movement : (x, y+1)
    • From this we can discern the following
      • Eastern movement : (x+1, y)
      • Southern movement : (x,y -1)
      • Western movement : (x-1,y)
    • We should use this is a case statement to change coordinates based on the current direction of the rover(s)

Input:

• The first line of input is the upper-right coordinates of the plateau, the lower-left coordinates are assumed to be 0,0.

• Assumptions :

  • Therefor the range from 0 - 5 is 6 units of change
  • Our array(plateau) size can then calculated with upper right x an y coords namely urx and ury
  • lenX = 0
  • lenY = 0
    • For x in range(0, urx):
      • lenX += 1
    • For y in range(0, ury):
      • lenY += 1
  • arraySize = lenX * lenY

• The rest of the input is information pertaining to the rovers that have been deployed.

  • Each rover has two lines of input.
  • The first line gives the rover's position,
  • The second line is a series of instructions telling the rover how to explore the plateau.

• The position is made up of two integers and a letter separated by spaces, corresponding to the x and y co-ordinates and the rover's orientation.

###Each rover will be finished sequentially, which means that the second rover won't start to move until the first one has finished moving.

Output:

The output for each rover should be its final co-ordinates and heading.

Test Input:

Plateau size is a 6x6 matrix given the start coordinates of 0,0

• 5 5

Rover 1 - Message

• Position / start - Line 1
  • 1 2 N
• Instruction - Line 2
  • LMLMLMLMM

Rover 2 - Message

• Position / start - Line 1
  • 3 3 E
• Instruction - Line 2
  • MMRMMRMRRM

Expected Output:

1 3 N

5 1 E

Create function for cardinal directions:

N = 0° / 360°
E = 90°
S = 180°
W = 270°

Define a rover state: I never used this :D

setState(rover)
    // state object, only changes one attribute at a time
    state = {
           x : rover.x,
           y : rover.y,
           h : rover.h
    }

Define turning as a function:

    // NOTE --> 360° = 0° 
    turnRover(h, turn):
        If turn R:
            h = h + 90
            // when h is 360°, we set it to 0° so that we get 90°(E) when adding 90°
            if h == 360:
                h = 0
        If turn L:
            // when h is 0°, we set it to 360° so that we get 270°(W) when subtracting 90°
            if h == 0:
                h = 360
            h = h - 90

Define moving as a function:

    moveRover(currentX, currentY, h):
        // integer array for our coordinates
        Switch h:
            Case N:
                state = [currentX, currentY+1, h)
            Case E:
                state = [currentX+1, currentY, h)
            Case S:
                state = (currentX, currentY-1, h)
            Case W:
                state = [currentX-1, currentY, h)

Interpret the instructions

• R = + 90° to current direction
• L = - 90° to current direction
• M = increase position in current heading by 1

Assumptions and observations

• Turning does not change coordinates only the rovers heading
• Moving changes rovers coordinates but not heading
• Can they go out of bounds?
  • We should not expect NASA to have rovers that go out of bounds
• If they collide?
  • do they stop?
  • explode?
  • Engineering team at NASA decided just to skip commands that where erroneous

Ways to solve problem :

1. create a loop that executes the following commands per rover for n amounts of rovers

   • Init the rover if the init coordinates are valid

2. create another loop within that splits the bytes of the command into separate instructions characters

    foreach char in command:
        if char L or R:
            turnRover(h, char)
        if char M:
            moveRover(x, y, h)
   

   • change the state of the current rover based on the type(turning/moving) of instruction byte
   • Output the coordinates and heading of the current rover