2D Array

int[][] exampleArray = {
    {"Hello", "World"},
    {"Java", "Array"}
};

This should be a String not an int

public class ArrayPractice {
    public static void main(String[] args) {
        // Write the code to declare and initialize the 2D array here
        int[][] myNumbers = new int[3][];
        myNumbers[1] = {1,2,3};
        myNumbers[2] = {4,5,6};
        myNumbers[0] = {7,8,9};
        // Print the array
        System.out.println(java.util.Arrays.deepToString(myNumbers));
    }
}

ArrayPractice.main(null)

[[1, 2, 3], [4, 5, 6], [7, 8, 9]]

String[][] hack = {
    {"Hello", "World"},
    {"Java", "Array"}
};

hack[1][0] = "Programming";

System.out.println(Arrays.deepToString(hack));

[[Hello, World], [Programming, Array]]

public class Main {
    public static void main(String[] args) {
        int find[][] = {
            {10, 20, 30},
            {40, 55, 60},
            {70, 80, 90},
        };

        int last = 0;
        int lastDiff = find[0][0];
        for (int i = 0; i<find.length; i++){
            for(int j = 0; j<find[i].length;j++){
                if(find[i][j] - last != lastDiff){
                    System.out.println("Value " + (find[i][j]) +" doesn't match the pattern"); 
                    last = last + lastDiff;
                }
                else {
                    last = find[i][j];
                }
                
            }
        }
    }
}
Main.main(null);

Value 55 doesn't match the pattern

public class Main {
    public static void main(String[] args) {
        int[][] array = { 
            {1,2,3},
            {4,5,6},
            {7,8,9}
        };

        findIndexOfTarget(array,9);
    }

    public static int[] findIndexOfTarget(int[][] array, int target){
            int rows = array.length;
            if (rows == 0) return new int[] {-1, -1};
            int cols = array[0].length;
            
            int left = 0;
            int right = rows * cols - 1;
            
            while (left <= right) {
                int mid = left + (right - left) / 2;

                System.out.println(mid);
                int midValue = array[mid / cols][mid % cols];
                
                if (midValue == target) {
                    return new int[] {mid / cols, mid % cols}; // Return the row and column index
                }
                if (midValue < target) {
                    left = mid + 1; // Move to the right half
                } else {
                    right = mid - 1; // Move to the left half
                }
            }
            
            return new int[] {-1, -1}; // Target not found 
    }
}
Main.main(null);

4
6
7
8

Homework hacks page

8.1

public class Main {
    public static void main(String[] args) {
        String[][] array = {
            {"My", "A"}, 
            {"AP", "Class"}, 
            {"CS", "Rocks!"}
        };
        
        for (int col = 0; col < array[0].length; col++) {
            for (int row = 0; row < array.length; row++) {
                System.out.print(array[row][col] + " ");
            }
        }
    }
}

Main.main(null);

THe answer to the multiple choice is B. We are looping through each collumn followed by each row.

8.2

public class GradeSearch {
    public static String searchGrade(String[][] grades, String name) {
       
        for (int row = 0; row < grades.length; row++){
            // fif the name we are trying to find matches the first item in row
            if (name == grades[row][0]){
                //then return the second item (the grade)
                return grades[row][1];
            }
        }
        return "Student not found";
    }

    public static void main(String[] args) {
        // Sample 2D array with names and grades
        String[][] grades = {
            {"John", "93"},
            {"Alice", "85"},
            {"Bob", "78"},
            {"Eve", "92"}
        };

        // Test the search function
        String nameToSearch = "Alice";
        String grade = searchGrade(grades, nameToSearch);
        System.out.println(nameToSearch + "'s grade: " + grade);

        nameToSearch = "Charlie";
        grade = searchGrade(grades, nameToSearch);
        System.out.println(nameToSearch + "'s grade: " + grade);
    }
}

// Execute the main method to see the output
GradeSearch.main(null);

Alice's grade: 85
Charlie's grade: Student not found