See Also

• Traffic Lights - one car
• Traffic Lights - multiple cars

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Overview

A character string represents a city road.

Cars travel on the road obeying the traffic lights..

Legend:

• . = Road
• C = Car
• G = GREEN traffic light
• O = ORANGE traffic light
• R = RED traffic light

Something like this:

CCC.G...R...

Rules

Simulation

At each iteration:

1. the lights change (according to the traffic light rules), then
2. the car moves, obeying the car rules

Traffic Light Rules

Traffic lights change colour as follows:

• GREEN for 5 time units... then
• ORANGE for 1 time unit... then
• RED for 5 time units....
• ... and repeat the cycle

Car Rules

• Cars travel left to right on the road, moving 1 character position per time unit

• Cars can move freely until they come to a traffic light. Then:

  • if the light is GREEN they can move forward (temporarily occupying the same cell as the light)
  • if the light is ORANGE then they must stop (if they have already entered the intersection they can continue through)
  • if the light is RED the car must stop until the light turns GREEN again

• It is illegal to queue across an intersection. In other words, DO NOT enter an intersection unless you can see there is safe passage through it and out the other side!

Kata Task

Given the initial state of the road, return the states for all iterations of the simiulation.

Input

• road = the road array
• n = how many time units to simulate (n >= 0)

Output

• An array containing the road states at every iteration (including the initial state)
• Note: If a car occupies the same position as a traffic light then show only the car

Notes

• There are 1 or more cars
• There are 0 or more traffic lights
• For the initial road state:
  • cars can start anywhere except in the middle of intersections
  • traffic lights are either GREEN or RED, and are at the beginning of their countdown cycles
• There are no reaction delays - when the lights change the car drivers will react immediately!
• If a car goes off the end of the road it just disappears from view
• There will always be some road between adjacent traffic lights
• If there is a traffic light at the end of the road then its exit is never blocked
• You cannot see beyond the car in front of you, so you cannot anticipate a gap that does not yet exist

Example

Run simulation for 16 time units

Input

• road = "CCC.G...R..."
• n = 16

Result

[
  "CCC.G...R...", // 0 initial state as passed
  ".CCCG...R...", // 1
  "..CCC...R...", // 2 show 1st car, not the green light
  "..CCGC..R...", // 3 2nd car cannot enter intersection because 1st car blocks the exit
  "...CC.C.R...", // 4 show 2nd car, not the green light
  "...COC.CG...", // 5 3rd car stops for the orange light
  "...CR.C.C...", // 6
  "...CR..CGC..", // 7
  "...CR...C.C.", // 8
  "...CR...GC.C", // 9
  "...CR...O.C.", // 10
  "....C...R..C", // 11 3rd car can proceed
  "....GC..R...", // 12
  "....G.C.R...", // 13
  "....G..CR...", // 14
  "....G..CR...", // 15
  "....O...C..."  // 16
]

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Good luck!

DM