AP CSA 4.1 Exercise 1: Report the Aggregate, Not the Person

Unit 4: Data Collections · Lesson 4.1 · Exercise 1

Report the Aggregate, Not the Person

Ethical and Social Issues Around Data Collection. Write real Java, run it, and submit it to be graded against hidden test cases.

Back to the Lesson 4.1 page All Unit 4 lessons

Why this one is worth doing

Data minimisation is a thing you write, not a thing you agree with. This program is handed identifying records and has to answer questions about the group without ever printing anything that points at one person.

What to write

Read an integer count, then that many records. Each record is an id number and then an age, on one line.
Print the number of records you read.
Print the average age as an integer, using integer division.
Print how many of the people were 18 or older.
Print the range, meaning the oldest age minus the youngest.
Print no id, and no individual age. The grader checks that the ids never appear in your output.

Your program reads

A count, then that many lines of two integers: an id and an age.

Your program prints

Four lines: the record count, the average age, the count of adults and the age range.

Worked examples

These are the cases you can see. There are more you cannot, and they use different values, so an answer that prints these numbers as constants will fail.

Example 1 input

Example 1 output

Example 2 input

1
900 18

Example 2 output

Your answer

Main.java

import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    int count = input.nextInt();

    // Read the ids, use none of them.
  }
}

Input for the Run button

Run sends whatever is in the input box below. Submitting runs your program against every test case, including hidden ones with different input.

Stuck?

Hint 1

You still have to READ the id to get past it to the age. Reading it and not keeping it is exactly the point.

Hint 2

The average is asked for as an integer, so plain int division is correct here and no cast is wanted.

Hint 3

Seed the oldest and youngest from the first record rather than from 0, or a data set of teenagers reports a youngest age of 0.

Where to go next

Rework the Lesson 4.1 page Pick another Unit 4 lesson

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