Unit 8 · Exam-weighted
The final unit combines grid traversal, the standard search and sort algorithms with their efficiency comparison, and the data topics that close the course.
What a strong answer looks like
A strong Unit 8 answer names which loop controls rows and which controls columns, and compares algorithms by how their work grows rather than by stopwatch.
Know
A 2D array is an array of arrays. The first index selects the row and the second the column, and rows need not all be the same length.
Apply
Use the outer length for the row count and each row’s own length for its column count.
Watch out
Assuming every row has the same length, which fails on a ragged array.
Study move
Declare a 2D array and state the expression giving the number of columns in a specific row.
Know
Row-major traversal puts the row loop outside and the column loop inside, visiting each row completely before moving on.
Apply
Name which loop controls rows before tracing, then count visits as the product of the bounds.
Watch out
Swapping the indexes, which either transposes the result or throws when the array is not square.
Study move
Trace a row-major sum and then a column-major sum of the same grid.
Know
Linear search works on any order; binary search requires sorted data and halves the remaining range each step.
Apply
Check that data is sorted before choosing binary search, and compute the midpoint safely.
Watch out
Applying binary search to unsorted data, which returns a confidently wrong answer rather than failing.
Study move
Trace a binary search on a sorted array, recording the range at each step.
Know
Selection and insertion sort compare and move elements repeatedly; their cost grows with the square of the input, while merge sort grows far more slowly.
Apply
Compare algorithms by counting comparisons as the input grows, not by timing one run.
Watch out
Claiming an algorithm is fast from one small example. Growth rate, not a single measurement, is what is being compared.
Study move
Count the comparisons insertion sort makes on already-sorted and reverse-sorted input.
Know
Scanner reads input token by token or line by line, and the reading pattern must match the shape of the data.
Apply
Check whether more input remains before reading, and match the read method to the data type.
Watch out
Mixing token and line reads, which leaves a partial line behind and misaligns everything after it.
Study move
Describe the reads needed for a file where each line holds a name and a number.
Know
Programs that collect data carry consequences for the people described by it, including privacy and the risk of encoding existing bias.
Apply
For any program handling personal data, state what is collected, why it is needed, and who can see it.
Watch out
Treating data questions as opinion. They expect reasoning about specific, identifiable consequences.
Study move
Take a small program that stores student records and list what it collects and what could go wrong.
Connections and techniques that receive extra attention in this unit.
Related topics some schools attach to this unit and others leave out. Covered on request rather than assumed.
Modeling drill
Write a traversal that finds the largest value in a 2D array and reports its row and column, then state its behavior on a ragged array.
