cs-010 — Rain or Shine
| Field | Value |
|---|---|
| id | cs-010 |
| difficulty | Foundational |
| topics | flowchart, decisions |
| lecture | lecture-03 |
| estimated time | 5-minute attempt + 10-minute discussion |
| prerequisites | lectures 1-2 (problem framing, precise pseudocode) |
| objective | recognise the pattern, translate it into precise steps, and trace it correctly |
| solution | held by the instructor; discussed after the attempt |
Problem
A garden watering system turns on based on rain sensor, time of day, and soil moisture. Build the decision flowchart and simplify redundant branches.
Your deliverable is the stated assumptions, the rule list, the decision for the worked instance, and one contested case. If the problem is ambiguous anywhere, state the assumption you are making and carry on — a stated assumption is part of a good answer.
Examples
- Input: rain no, 14:00, moisture 22% (threshold 30%)
- Output: water on (dry soil overrides afternoon ban); rain yes -> off regardless
Solve for the worked instance first. Then ask what would change if one number, name, or condition were replaced by something stranger.
What to notice
- List the sensors, write the condition as one Boolean sentence, then look for redundant branches.
- Writing the rules IS the solution; code is transcription.
- Every assumption is a place where two good answers can differ.
Discussion starter
After the solution is revealed, the class spends five minutes on this prompt: "Which assumption would you attack first if you had to argue the other side?"
Constraints and assumptions
- Difficulty: Foundational (early-semester techniques assumed: precise statements, traces, simple loops).
- Topics: flowchart, decisions.
- Classroom-scale inputs unless the problem says otherwise.
- Time-box: about five minutes; naming the pattern and stating the assumption is already a pass, completing the calculation is the stretch.
- Optional stretch (not required): describe an alternative approach and say when it beats the obvious one.
Hints and extension
- First nudge: identify the pattern the worked instance uses before computing anything.
- If stuck after three minutes, write the input/output line you expect and trace the smallest example by hand.
- After the reveal, attempt the extension below before the next lecture.
- Extension challenge: Redraw the flow with one extra decision diamond and argue what changes.