Rules: Place a digit from 1-7, or blacken in each cell such that each digit appears exactly once in each row, column and marked 3×3 box. There will be 2 blackened cells in each row, column and 3×3 box. Numbers outside the grid indicate the total of cells between the blackened cells in the corresponding direction.
Background: This is one of my design. Actually, it is Smashed Sums + Sudoku.