AP CSA 4.13 FRQ Practice: Finding in a Grid

Unit 4: Data Collections · Lesson 4.13 · FRQ Practice

Finding in a Grid

A free response question in the shape the exam uses: a stated contract, four rubric parts, and no main method handed to you. Worth 4 points.

Back to the Lesson 4.13 pageAll Unit 4 lessons

Why this question is worth four points

Searching a grid means returning WHERE something is, and a position is two numbers. This question asks for the row and the column separately so that a transposed answer is visibly wrong rather than accidentally right.

What you are given

The driver builds a rectangular 2D int array and passes it to your methods. Write a class named Search2D. Do not write a main method.

The question

  1. (a) public static int maxValue(int[][] grid) returns the largest value anywhere in the grid.
  2. (b) public static int rowOfMax(int[][] grid) returns the row index of the largest value, choosing the earliest in row major order on a tie.
  3. (c) public static int colOfMax(int[][] grid) returns the column index of that same cell.
  4. (d) public static int countEqual(int[][] grid, int target) returns how many cells hold target.

What the reader is looking for

  1. Write class Search2D with the four static methods described. No main method.
  2. Seed the search with the cell at row 0 column 0, never with 0.
  3. Parts (b) and (c) must describe the SAME cell. Searching twice invites them to disagree on a tie.

Worked examples

These show what a correct answer prints. There are more cases you cannot see, and they use different values, so an answer built around just these numbers will fail.

Example 1 input
2 3
1 9 3
4 5 6
9
Example 1 output
9
0
1
1
Example 2 input
2 4
7 2 7 1
3 4 5 6
7
Example 2 output
7
0
0
2

Your answer

Main.java

Input for the Run button

How this is scored: your answer runs against every test case, and the fraction it passes becomes your score out of 4. That is not how a human AP reader marks a rubric, so treat the score as a check on whether your code works, and the rubric above as the thing you are actually practising.


  

  
Stuck?

    
Hint 1
Track the best POSITION rather than the best value, then read the value back out of the grid. That keeps parts (a), (b) and (c) describing one cell.

    
Hint 2
A strict greater-than keeps the first cell found in row major order, which is what the tie breaking rule asks for.

    
Hint 3
Seeding at grid[0][0] rather than 0 matters here for the same reason it did in 4.2: the grid may be entirely negative.



  
Before you submit

  
3 mistake(s) that lose points on this question
    
Each of these is a real error the grader catches. Check your answer against them before you submit, not instead of trying.

    
    
      
  • the search replaces on a tie, so it reports a later cell than the rule asks for
    • 
      
  • part (c) returns the row rather than the column
    • 
      
  • part (d) misses the last column of every row
    • 
    

  


  
Where to go next

  

    Rework the Lesson 4.13 page
    Try the from-scratch exercise for this lesson
    Try the debugging exercise for this lesson
  


  
  






  

















  
Get in Touch

  
Whether you're a student, parent, or teacher — I'd love to hear from you.







  
Just want free AP CS resources?

  

    Enter your email below and check the subscribe box — no message needed.
    Students get daily practice questions and study tips. Teachers get curriculum resources and teaching strategies.
  







  
  Typically responds within 24 hours






  
✓

  
Message Sent!

  

    Thanks for reaching out. I'll get back to you within 24 hours.
  







  


  

    
    

    
    

      

        
        
      

      

        
        
      

    


    
    

      

        
        
      

      

        
        
      

    


    
    

      

        
        
      

      

        
        
      

    


    
    

      
🏫 Welcome, fellow educator!

      

        I offer curriculum resources, practice materials, and study guides designed for AP CS teachers.
        Let me know what you're looking for — whether it's classroom materials, a guest speaker,
        or Teachers Pay Teachers resources.
      

    


    
    

      
      
    


    
    

    
    

      
    

  







  

    ✉
    
Email

    
[email protected]

  

  

    📚
    
Courses

    
AP CSA, CSP, & Cybersecurity

  

  

    ⏱
    
Response Time

    
Within 24 hours

  







  Prefer email? Reach me directly at
  [email protected]