FRQ QUESTION 3

public class SparseArrayEntry {
    private int row;
    private int col;
    private int value;

    public SparseArrayEntry(int r, int c, int v) {
        row = r;
        col = c;
        value = v;
    }

    public int getRow() {
        return row;
    }

    public int getCol() {
        return col;
    }

    public int getValue() {
        return value;
    }
}

public class SparseArray {
    private int numRows;
    private int numCols;
    
    private List<SparseArrayEntry> entries;
    public SparseArray(){ 
        entries = new ArrayList<SparseArrayEntry>(); 
    }
    public int getNumRows(){ 
        return numRows; 
    }
    public int getNumCols(){ 
        return numCols; 
    }
    public void setNumRows(int numRows) {
        this.numRows = numRows;
    }
    
    public void setNumCols(int numCols) {
        this.numCols = numCols;
    }
    
    public void addEntry(SparseArrayEntry entry) {
        entries.add(entry);
    }
    // Part A
    public int getValueAt(int row, int col)
    {
        for(SparseArrayEntry entry : entries)
            if(entry.getRow() == row && entry.getCol() == col)
                return entry.getValue();
    
        return 0;
    }
    // Part B
    public void removeColumn(int col) {
        for(int i = entries.size() - 1; i >= 0; i--) {
            SparseArrayEntry entry = entries.get(i);

            if(entry.getCol() == col)
                entries.remove(i);
            else if(entry.getCol() > col)
                entries.set(i, new SparseArrayEntry(
                        entry.getRow(), entry.getCol() - 1, entry.getValue()));
        }
        numCols--;
    }
    
    public static void main(String[] args) {
        SparseArray sparse = new SparseArray();

        sparse.setNumRows(4);
        sparse.setNumCols(4);

        sparse.addEntry(
            new SparseArrayEntry(0, 1, 1)
        );
        sparse.addEntry(
            new SparseArrayEntry(1, 2, 2)
        );
        sparse.addEntry(
            new SparseArrayEntry(2, 3, 3)
        );
        sparse.addEntry(
            new SparseArrayEntry(3, 1, -9)
        );

        System.out.println("Value at (3,1) before removing column: " + sparse.getValueAt(3, 1));
        System.out.println("Value at (2,3) before removing column: " + sparse.getValueAt(2, 3));

        System.out.println("Number of columns before removing one: " + sparse.getNumCols());
        sparse.removeColumn(1);

        System.out.println("Value at (3,0) after removing column: " + sparse.getValueAt(3, 0));
        System.out.println("Value at (2,2) after removing column: " + sparse.getValueAt(2, 2));

        System.out.println("Number of columns after removing one: " + sparse.getNumCols());
    }
} 

SparseArray.main(null)

Part A: getValueAt Method: This method is designed to get the value at a specific row and column in the sparse array. It iterates through the list of SparseArrayEntry objects and checks if the entry’s row and column match the specified row and column. If a match is found, it returns the value of that entry; otherwise, it returns 0.
Part B: removeColumn Method: This method removes a specified column from the sparse array. It iterates through the list of entries backward (from the end to the beginning) to avoid issues with modifying the list while iterating. If an entry has the specified column, it is removed from the list. If the entry’s column is greater than the specified column, it is updated by decrementing the column by 1. After removing entries related to the specified column, the number of columns (numCols) is decremented.