�AP Java 2D Arrays

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Warm up Kahoot: 8775687

Essential Questions

• How do you create and use a 2D array?

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Learning Target

Be able to use a 2D array in solving a challenge.

Outline

• Review Kahoot
• AP Practice questions for 2D arrays

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What is the value of sum are the code is executed?

2-D Arrays: Dimensions

• In Java, a 2-D array is a 1-D array of 1-D arrays, its rows. Each row is stored in a separate block of consecutive memory locations.
• If m is a 2-D array, then m[k] is a 1-D array, the k-th row.
• m.length is the number of rows.
• m[k].length is the length of the k-th row.

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More Two D

• Internally, Java stores 2 dimensional arrays as an array of arrays:
• int [][] nums = new int[5][4];
• The above is really equivalent to a 3-step process:
• // create the single reference nums (yellow square)
• int [][] nums;
• // create the array of references (blue squares)
• nums = new int[5][];
• // this create the second level of arrays (red squares)
• for (int i=0; i < 5 ; i++)
• nums[i] = new int[4]; // create arrays of integers

Tic-Tac-Toe

• Write a program that will model playing Tic-Tac-Toe using a 2D array to store the x’s, blanks, and O’s.
• The program needs to let each user have a turn
• The user can determine if the game is over
• Push: Computer vs. user
• Push: Using logic so the computer will never lose.

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Magic Square

• A magic square[1] is a n by n square grid (where n is the number of cells on each side) filled with distinct positive integers in the range {1,2,...,n²} such that each cell contains a different integer and the sum of the integers in each row, column and diagonal is equal

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Magic Square Program

• Level 1: Write a program that will take as input the values for each cell of a 3x3 potential magic square and determine if the square is magic.
• Level 2: Write a program to generate 3x3 magic squares. Using an algorithm rather than just hard coding a found solution.
• Level 3: Modify this to handle n x n magic squares where n is an odd number. (See Google Doc describing an algorithm on the class website.)

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