2-6

class Solution {
    public int[][] construct2DArray(int[] original, int m, int n) {
        if (original.length != m * n) {
            // Impossible. Return an empty 2D array.
            return new int[0][0];
        }
        int[][] result = new int[m][n];
        for (int i = 0; i < original.length; i++) {
            result[i / n][i % n] = original[i];
        }
        return result;
    }
}



class Solution {
    public int[][] construct2DArray(int[] original, int m, int n) {
        if (original.length != m * n) {
            return new int[0][0];
        }
        int[][] arr = new int[m][n];
        int current_index = 0;
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                arr[i][j] = original[current_index];
                current_index++;
            }
        }
        return arr;
    }
}