Take-home Lab 1. Arrays

Transcription

1 Take-home Lab 1 Arrays

2 Findx 2-Dimensional Array Graded! Submit by Friday 23:59

3 Find You are given a treasure map by your friend Map is divided into R by C cells Super Marks The Spot You need to find all the Super in the map Square of size at least 3 Composed entirely by on both diagonals If you find all the Super, you get the treasure

4 How many Super? 7

5 How many Super? 7 Square of size 3

6 How many Super? 7 Square of size 3

7 How many Super? 7 Square of size 4

8 How many Super? 7 Square of size 5

9 How many Super? 7 Square of size 5

10 How many Super? 7 Square of size 6? No Super

11 How many Super? 7 Square of size 7 Total: 6

12 Planning 1. Read input Map dimensions and the map itself 2. Count all the Super Create a method to find it 3. Output answer The number of Super

13 Input Two integers Dimensions of the map R: the number of cows C: the number of columns R lines of characters One line has C characters Characters are either or.

14 Reading the input Initialise the scanner Scanner sc = new Scanner(System.in) Read the first integer int numrows = sc.nextint() Read the next integer int numcols = sc.nextint() Initialise the map char[][] map = new char[numrows][numcols] Read all the lines for (int i = 0; i < numrows; i++) String row = sc.next() map[i] = row.tochararray()

15 Counting all the Super Place your code in its own method int countsuper(char[][] map, int numrows, int numcols) Break the problem down to smaller sub-problems For each of the possible square sizes Iterate through every cell, using it as the top-left corner of a possible Super square of the current square size Check whether that square is really a Super If it is, add 1 to the total Super count Return the total Super count as an integer

16 Iterating through the map 7

17 Iterating through the map 7

18 Iterating through the map 7

19 Iterating through the map 7

20 Iterating through the map 7

21 Iterating through the map 7

22 Iterating through the map 7

23 Iterating through the map 7

24 Is it a Super? Given a square size and the top-left cell, we are able to check whether it is a Super boolean issuper(char[][] map, int size, int currrow, int currcol) What defines a Super? Square of size at least 3 Composed entirely by on both diagonals First check the square size Return false if square size less than 3 Then check the diagonals Return true if both diagonals are composed of all

25 Diagonal Checking x 7 Super 6 x 6 Super

26 Diagonal Checking Left diagonal Start at the top left corner Go down to the bottom right corner Right diagonal Start at the top right corner Go down to the bottom left corner Write two methods to check them boolean isleftdiagonalall(map, size, currrow, currcol) boolean isrightdiagonalall(map, size, currrow, currcol)

27 Checking the Left Diagonal Let r be currrow Let c be currcol For i from 0 to squaresize If map[r][c] is Go to next cell on the diagonal Else Return false

28 Checking the Right Diagonal Let r be currrow Let c be currcol + squaresize - 1 For i from 0 to squaresize If map[r][c] is Go to next cell on the diagonal Else Return false

29 Finally, display output Simply print the number of Super System.out.println(countSuper(map, numrows, numcols)) Don t print anything else!

30 Questions?

31 Island 2-Dimensional Array

32 Island You are given a map of Hyrule, a land of many islands Map is divided into R by C cells You need to find all the islands in Hyrule Rectangle of at least size 2 Composed entirely of 1 Surrounded entirely by 0 Count the total number of islands

33 Islands of Hyrule

34 Islands of Hyrule

35 Islands of Hyrule

36 Islands of Hyrule

37 Islands of Hyrule

38 Planning 1. Read input Map dimensions and the map itself 2. Count all the islands Create a method to count the islands 3. Output answer The number of islands

39 Input Two integers Dimensions of the map R: the number of cows C: the number of columns R lines of characters One line has C characters Characters are either 1 or 0

40 Reading the input Initialise the scanner Scanner sc = new Scanner(System.in) Read the first integer int numrows = sc.nextint() Read the next integer int numcols = sc.nextint() Initialise the map char[][] map = new char[numrows][numcols] Read all the lines for (int i = 0; i < numrows; i++) String row = sc.next() map[i] = row.tochararray()

41 Counting islands Place your code in its own method int countislands(char[][] map, int numrows, int numcols) How to find? Iterate through every cell from top to bottom, using it as the top-left corner of a possible island If the cell contains a 1, it is definitely the top-left of an island Increase the total island count by one Set all the island s 1 to 0 to prevent double counting Return the total island count as an integer

42 Counting islands

43 Counting islands

44 Counting islands

45 Counting islands

46 Counting islands

47 Counting islands

48 Counting islands

49 Counting islands

50 Counting islands lazy way All islands have this pattern on their top left corner Once you see that pattern, you know it is an island But what if an island starts on the edge of the map? Add a dummy row and column of 0 to the top and left of the map Now there will be no islands that start on the edge of the map

51 Counting islands lazy way Find this pattern

52 Counting islands lazy way Add dummy row and column

53 Counting islands lazy way Find this pattern

54 Counting islands lazy way Find this pattern

55 Counting islands lazy way Find this pattern

56 Counting islands lazy way Find this pattern

57 Finally, display output Simply print the number of islands System.out.println(countIslands(map, numrows, numcols)) Don t print anything else!

58 Questions?

59 Measurement Calculation and Formatting

60 Measurement You are a teacher that needs to take students measurements You are given a list of students names, heights and weights You are to find the shortest and tallest students For these students, you are also required to find their BMI

61 Planning 1. Read input Number of students and their information 2. Find the shortest student and his BMI 3. Output the information 4. Find the tallest student and his BMI 5. Output the information

62 Input Integer N, the number of students N lines of student information, consisting of: String name Integer height Integer weight

63 Reading the input Initialise the scanner Scanner sc = new Scanner(System.in) Read the first integer int numstudents = sc.nextint() Store the information in three separate arrays String[] names; int[] heights; int[] weights; Read all the lines for (int i = 0; i < numstudents; i++) names[i] = sc.next() heights[i] = sc.nextint() weights[i] = sc.nextint()

64 Shortest Student Go through the height array and keep the index of the smallest number Use that index to get the name and weight of the corresponding student Calculate the BMI of the student Output the required information Use similar steps to find the tallest student s information

65 Without using arrays We don t absolutely need arrays for this problem While reading the input, keep track of the shortest and tallest students at the same time Also store their height and weight Once you finish reading the input, just calculate the BMI of both students You end up using less storage space, but it is easy to make careless mistakes

66 Calculating BMI BMI is not guaranteed to be a whole number, hence we have to store it as a float or double type double bmi; However weight and height were stored as integers, so we need to convert them to double as well double heightforbmi = height / 100 double weightforbmi = weight double bmi = weightforbmi / (heightforbmi * heightforbmi) Alternatively, we could have read them in as a double from the start sc.nextdouble()

67 Printing two decimal places If you want a String representation in two decimal places, use: String.format( %.2f, bmi) If you just want to directly print it, use: System.out.printf( %.2f, bmi) Note that printf does not give a newline at the end of the output You will need to add your own newline Read this link for more information

68 Output Construct your output like this String outputshortest = String.format( %s is the shortest with BMI equals to %.2f., name, bmi) Input the name and the calculated bmi in the correct order System.out.println(outputShortest) Read this simple formatting guide Can be used for both String.format() and System.out.printf()

69 Questions?