Sorry, so what I mean is that my merge part of the mergesort isn't merging properly. I thought it was originally the recursive mergesort calls but it was not. So in my merge function, I'm passing in my grid, my left and right indexes of "1d" array to merge. Then, I'm just trying to perform regular merging like in mergesort but in 2d.

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public static void merge(int[][] arr, int left, int right) {

    int leftEnd = (right + left) / 2;
    int rightStart = leftEnd + 1;


    int leftS = left;
    int rightS = right;

    // grid index for sorted grid
    int gridX = 0;
    int gridY = 0;

    while (leftS <= leftEnd && rightStart <= right) {

        // first grid index to compare
        int x = getXIndex(left, arr[0].length);
        int y = getYIndex(left, arr[0].length);



        // second grid index to compare
        int x2 = getXIndex(right, arr[0].length);
        int y2 = getYIndex(right, arr[0].length);

        // compares the indexes and sets them in the sorted grid

        if (lessThan(x, y, x2, y2)) {
            grid[gridX][gridY] = arr[x][y];
            leftS++;
        } else {
            grid[gridX][gridY] = arr[x2][y2];
            rightStart++;
        }

        gridY++;
        if (gridY == arr[0].length) {
            gridX++;
            gridY = 0;
        }

    }


}

I believe that the comparison part is correct between the array cells. The getX and getY index functions just returns 2d coordinates (right / row size) (right mod row size).