Code Kata: toy fleet management

Background: there is an infinite grid with one point selected as a fleet management centre. There is a number (> 1) of cars that move through the grid, one step at a time, only in up, down, left and right directions. The cars periodically send their position on the grid to the management centre.

The task: we are to write a program that accepts coordinates sent by the cars and then can tell us the current total distance travelled by a car.

Points to consider: we assume that the coordinates are send periodically, regardless of the car's movement. Thus, a car may send various series of coordinates that our program must be able to interpret. Tip: the calculated total distance will be an approximation, not an exact value.

Additional functions (to be done as a next step, do not bring it outright into the design): if a car travels away from the management centre farther than N units, the program will signal that fact. Just use any method you wish to signal this, but remember that it should not be annoying, in case a driver took a long trip on the countryside.