Unit 11: Data structures

Question 1

What is a data structure in programming?

Answer 1

A way of organizing and storing data so it can be accessed and modified efficiently.

Question 2

What two things usually go together in program design?

Answer 2

The choice of data structures and the algorithms used to process them.

Question 3

What are parallel arrays?

Answer 3

Multiple arrays used to represent a single group of records, where each array stores a different field.

Question 4

Example use of parallel arrays?

Answer 4

An address book with names[], addresses[], and phoneNumbers[], where index i across all arrays relates to one person.

System.out.println(name[i] + " " +
address[i] + " " + phone[i]);

Question 5

What is a partially filled array?

Answer 5

A fixed-size array where only some elements are actively used. The rest of the array is unused but available for future data.

Question 6

Why are partially filled arrays useful?

Answer 6

They allow flexibility within fixed-size arrays, helping manage memory while tracking only the meaningful (used) data.

Question 7

What variable is typically used alongside a partially filled array?

Answer 7

currentSize – the index of the first unused element.

Question 8

What is the boolean inUse[] array used for?

Answer 8

It tracks which indices of the main array actually hold valid data (true) and which don’t (false).

Question 9

Advantage of using inUse[] over currentSize?

Answer 9

No need to shuffle on deletion; the position is simply marked as not in use.

Question 10

How do you mark all array positions as unused?

Answer 10

for (int i = 0; i < size; i++) inUse[i] = false;

Question 11

How do you count the number of used elements?

Answer 11

int count = 0;
for (int i = 0; i < size; i++)
    if (inUse[i]) count++;

Question 12

How do you mark a value as deleted?

Answer 12

inUse[i] = false;

Question 13

How do you insert a new value?

Answer 13

for (int i = 0; i < size; i++) {
    if (!inUse[i]) {
        data[i] = value;
        inUse[i] = true;
        break;
    }
}

Question 14

How do you find a value in a partially filled array?

Answer 14

for (int i = 0; i < size; i++)
    if (inUse[i] && data[i] == value) return i;
return -1;