复制2D数组并增加大小以填充新值

Question

I would like to first apologize if my question is worded badly. I have an exam tmmrw and the prof gave a sample final exam for us to practice with. He unfortunately isn't responding with the solutions on the forum so I am trying to provide solutions on there. I seem to be stuck on this question. I have to write a method that accepts and NxM array filled with integer values as a parameter. The method is to return an (N+1)x(M+1) array which contains the contents of the original array in the first N rows and M columns plus a count of items greater than or equal to zero in each row/column at the end of that row/column and put the value -1 in the bottom right corner. for example.

    1 -2  0              returns          1 -2  0  2
    3 -4 -5                               3 -4 -5  1
                                          2  0  1 -1

I seem to be able to copy the array yet I am puzzled as to how I can enter the values in the outer parts of the new array. Here is what I have so far.

public static void main(String[] args) {

        int[][] arr = { { 1, -2, 0 }, { 3, -4, -5 } };

        int[][] newMatrix = processing2D(arr);

        printArray(newMatrix);

    }

    //Method where I am having problems
    public static int[][] processing2D(int[][] arr) {

        int[][] matrix = new int[arr.length][arr[0].length];

        for (int row = 0; row < matrix.length; row++) {

            for (int col = 0; col < matrix[0].length; col++) {

                // once I reach the last pos I enter the count
                // of numbers greater than or equal to zero in that row/col

                matrix[row][col] = arr[row][col];

            }

        }

        // assign the corner -1 here

        return matrix;
    }

    public static void printArray(int[][] list) {

        for (int row = 0; row < list.length; row++) {
            for (int col = 0; col <= list.length; col++) {
                System.out.print(list[row][col] + " ");
            }
            System.out.println();
        }

    }

Answer 1

First off you are initializing the new array wrong it should be

int[][] matrix = new int[arr.length+1][arr[0].length+1];

You don't want it to be the same length you want it to be the length +1. Also in your for loops you want to go by the length of arr not matrix since thats what you're taking from. While putting the values into the new N+1xM+1 array, increment the value of the corresponding last element in that row and column by 1 if it is >=0.

for (int row = 0; row < arr.length; row++) {

        for (int col = 0; col < arr[0].length; col++) {

            // once I reach the last pos I enter the count
            // of numbers greater than or equal to zero in that row/col
            if(arr[row][col]>=0){
              matrix[row][matrix[row].length-1] = matrix[row][matrix[row].length-1] + 1;

              matrix[matrix.length-1][col]= matrix[matrix.length-1][col] + 1;
            }


            matrix[row][col] = arr[row][col];

            }

After putting all the values back into the new N+1xM+1 array you should now take the values in the n sized and m sized arrays and put them into the corresponding slot in the N+1xM+1 array. After that just put the -1 in the bottom right slow manually.

matrix[matrix.length-1][matrix[0].length-1]=-1;

Answer 2

In your process2D method start off by creating an array with the correct size which has 1 more row and 1 more column than the original:

int[][] matrix = new int[arr.length+1][arr[0].length+1];

Then to populate the matrix array you do like you were doing before, but you need to take care not to reference an index of the arr array that is out of bounds. Because your matrix index is bigger than arr. If you are populating the new indexes then you can just use random numbers.

        if(row < arr.length && col < arr[0].length)
        {
            matrix[row][col] = arr[row][col];
        }
        else
        {
            matrix[row][col] = new Random().nextInt(10);
        }

So here is the full method process2D:

public static int[][] processing2D(int[][] arr) {

    int[][] matrix = new int[arr.length+1][arr[0].length+1];

    for (int row = 0; row < matrix.length; row++) {

        for (int col = 0; col < matrix[0].length; col++) {

            // once I reach the last pos I enter the count
            // of numbers greater than or equal to zero in that row/col
            if(row < arr.length && col < arr[0].length)
            {
                matrix[row][col] = arr[row][col];
            }
            else
            {
                matrix[row][col] = new Random().nextInt(10);
            }

        }

    }

    // assign the corner -1 here

    return matrix;
}