X-Sum Sudoku

X-Sum is an exciting puzzle variant that includes numbers outside the grid. These numbers can appear above, below, to the left, and/or to the right of the grid.

X-Sum Rule: The numbers outside the grid indicate the sum of the first X cells from that viewpoint, where X corresponds to the value of the first cell in that direction.

Refer to the image above for examples. X-Sums accompanied by a thumbs up are correct examples, while those with thumbs down are incorrect. In Column 4, the sum is 17, and the closest cell to the sum is 4, indicating that the sum of the first 4 cells must be 17. Indeed, the first 4 cells are 4, 5, 7, and 1, which sum up to 17. In Row B, the X-Sum on the right side is 18, and the closest cell to the sum is 3. The first 3 digits are 3, 7, and 9, which sum up to 19; therefore, it is incorrect.