[PDF] [PDF] Topic 26 Two Dimensional Arrays - UT Austin Computer Science

[PDF] Two-Dimensional Arrays

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[PDF] Topic 26 Two Dimensional Arrays - UT Austin Computer Science

Jeffery Ullman Based on slides for Building Java Programs by Reges/Stepp, found at Write a method to find the max value in a 2d array of ints Write a 

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Topic 26

Two Dimensional Arrays

"Computer Science is a science of abstraction -creating the right model for a problem and devising the appropriate mechanizable techniques to solve it." -Alfred Aho and Jeffery Ullman Based on slides for Building Java Programs by Reges/Stepp, found at

2D Arrays in Java

Arrays with multiple dimensions may be

declared and used int[][] mat = new int[3][4]; the number of pairs of square brackets indicates the dimension of the array. by convention, in a 2D array the first number indicates the row and the second the column 2

Two Dimensional Arrays

0 1 2 3 column

0 1 2 row 0000 0000 0000 This is our abstract picture of the 2D array and treating it this way is acceptable. (actual implementation is different) mat[2][1] = 12; 3

What is What?

int[][] mat = new int[10][12]; // mat is a reference to the whole 2d array // mat[0] or mat[r] are references to a single row // mat[0][1] or mat[r][c]are references to // single elements // no way to refer to a single column // mat.length is the number of rows // mat[0].length is the number of columns // in row 0. 4

2D Array Problems

Write a method to find the max value in a 2d array of ints Write a method that finds the sum of values in each column of a 2d array of doubles

Write a method to print out the elements of a 2d

array of ints in row order. row 0, then row 1, then row 2 ...

Write a method to print out the elements of a 2d

array of ints in column order column 0, then column 1, then column 2 ... 5

Clicker 1

What is output by the following code?

String[][] strTable= new String[5][8];

System.out.print(strTable.length+ " ");

System.out.print(strTable[0].length + " ");

A.40 0 0

B.8 5 0

C.5 8 0

D.5 8 then a runtime error occurs

E.No output due to a syntax error.

6

Use of Two Dimensional Arrays

2D arrays are often used when I need a

table of data or want to represent things that have 2 dimensions.

For instance an area of a simulation

7

Example of using a 2D array

Conway's Game of Life

a cellular automaton designed by John Conway, a mathematician not really a game a simulation takes place on a 2d grid each element of the grid is occupied or empty 8

Simulation

Select pattern from menu

Select region in large area with mouse by

pressing the control key and left click at the same time

Select the paste button

9

Generation 0

0 1 2 3 4 5

0 1 2 3 * indicates occupied, . indicates empty 10 Or

0 1 2 3 4 5

0 1 2 3 11

Generation 1

0 1 2 3 4 5

0 1 2 3 * indicates occupied, . indicates empty 12

Or , Generation 1

0 1 2 3 4 5

0 1 2 3 13

Rules of the Game

If a cell is occupied in this generation.

it survives if it has 2 or 3 neighbors in this generation it dies if it has 0 or 1 neighbors in this generation it dies if it has 4 or more neighbors in this generation

If a cell is unoccupied in this generation.

there is a birth if it has exactly 3 neighboring cells that are occupied in this generation

Neighboring cells are up, down, left, right,

and diagonal. In general a cell has 8 neighboring cells 14

Clicker 2

Implement a program to run the

simulation

What data type do you want to use for

the elements of the 2d array?

A.String

B.char

C.int

D.boolean

E.double

15

Clicker 3

Do you want to use a

buffer zone on the edges? A.No B.Yes 16quotesdbs_dbs4.pdfusesText_7