AP CSA FRQ Guide
2013 FRQ 4: SkyView
Load one-dimensional telescope scan data into a 2D view using alternating row direction, then average a rectangular region.
2D Array Construction and Averaging22 minute target2D arraysconstructorsaveragesindexing
Skills Tested
What this FRQ is really practicing
2D arraysconstructorsaveragesindexing
Treat these skills as the study checklist. If any tag feels shaky, review that topic before attempting the full written response.
Starter Approach
How to begin without copying a solution
- 1Constructor: fill each row left-to-right or right-to-left according to scan order.
- 2Method: sum values in an inclusive row/column rectangle and divide by the number of values.
Write a first attempt before revealing any solution outline. Most AP CSA FRQ progress comes from tracing your own code and finding the missing case.
Common Mistakes
Mistakes to watch for while writing
Filling every row left to right.
Dividing by rows plus columns instead of the number of cells.
Using exclusive end indexes for the rectangle.
Self Check
Review questions before you submit
Allocates the 2D view array.
Use numRows and numCols.
Tracks the current index in scanned.
Use a separate index as values are copied.
Handles alternating row direction.
Odd and even rows fill in opposite directions.
Averages all values in the inclusive rectangle.
Loop from start through end for both rows and columns.
Practice Links