AP CSA 4.5 Exercise 1: Four Standard Algorithms

Unit 4: Data Collections · Lesson 4.5 · Exercise 1

Four Standard Algorithms

Algorithms with Arrays. Write real Java, run it, and submit it to be graded against hidden test cases.

Back to the Lesson 4.5 page All Unit 4 lessons

Why this one is worth doing

These four turn up on the exam in some form every year. Writing them once from an empty editor is worth more than reading them ten times.

What to write

Read an integer count, then that many integers into an array.
Print the sum of all the elements.
Print the average as a double, so a whole number still shows a decimal point.
Print how many elements are strictly greater than that average.
Print true when the array is in non decreasing order, and false otherwise.
Print the number of pairs of neighbouring elements that are equal.

Your program reads

An integer count of at least 1, then that many integers.

Your program prints

Five lines: the sum, the average, the count above average, the sorted check and the equal neighbour count.

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

5
4 7 2 9 1

Example 1 output

23
4.6
2
false
0

Example 2 input

4
1 2 2 5

Example 2 output

10
2.5
1
true
1

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();
    int[] data = new int[count];
    for (int i = 0; i < count; i++) {
      data[i] = input.nextInt();
    }

    // Five answers. Two of them compare neighbours.
  }
}

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

Cast the sum to double before dividing, or the average of 7 and 2 comes out as 4.0 instead of 4.5.

Hint 2

A neighbour comparison starts at i = 1 and looks back at i - 1, so it never reads past either end.

Hint 3

A one element array is sorted and has zero equal pairs. The loop simply does not run, which is the right answer.

Where to go next

Rework the Lesson 4.5 page Pick another Unit 4 lesson

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