Goal. Fill every white square with a digit from 1 to 9 so that each run adds up to its clue.
Clues and runs
A run is a line of white squares across or down. Its clue sits in the dark square before it: the number with → is for the run to the right, the one with ↓ for the run below.
The digits of a run add up to its clue.
A digit never repeats within one run. Runs with a repeat or a wrong total are marked.
Small totals. A total of 3 in two squares must be 1 + 2, and a total of 4 must be 1 + 3, since 2 + 2 repeats. The ringed square lies in a 4-run across and a 3-run down, so it must be 1, and the rest follows.
Help
Every grid has exactly one solution. Hint reveals the selected square, or the first empty or wrong one.
Controls
Select a square, then use the number pad or press 1–9. Backspace or 0 clears. Arrow keys move between squares.