AP CSA 4.12 Exercise 1: Across, Down, Diagonal

Unit 4: Data Collections · Lesson 4.12 · Exercise 1

Across, Down, Diagonal

Traversing 2D Arrays. Write real Java, run it, and submit it to be graded against hidden test cases.

Back to the Lesson 4.12 pageAll Unit 4 lessons

Why this one is worth doing

Row major order is the default and column major order is the one that catches people out, because it needs the loops in the opposite nesting from the one that feels natural.

What to write

  1. Read rows and cols, then the grid values in row order.
  2. Print all values in ROW major order, one per line: every value of row 0, then every value of row 1, and so on.
  3. Print all values in COLUMN major order, one per line: every value of column 0 top to bottom, then column 1, and so on.
  4. Print the sum of every value.
  5. Print the largest value anywhere in the grid.

Your program reads

Two integers, rows and cols, then rows times cols integers in row order.

Your program prints

Every value row major, then every value column major, then the total and the maximum.

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
2 3
1 2 3
4 5 6
Example 1 output
1
2
3
4
5
6
1
4
2
5
3
6
21
6
Example 2 input
1 4
7 8 9 10
Example 2 output
7
8
9
10
7
8
9
10
34
10

Your answer

Main.java

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
Column major order puts the COLUMN loop on the outside. The subscript is still grid[r][c], only the nesting changes.

    
Hint 2
The enhanced for over a 2D array gives you a whole row at a time, so it takes two of them: for (int[] row : grid) then for (int value : row).

    
Hint 3
Seed the maximum with grid[0][0] rather than 0, or a grid of negatives reports 0.


  
Where to go next

  

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