This puzzle is part of the Puzzling Stack Exchange Advent Calendar 2023. The accepted answer to this question will be awarded a bounty worth 50 reputation.
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Task: Solve the killer sudoku
Solved grid:
It was fun!
General solve path:
Start with the obvious one box clue R3C5 and R8C7, then to the 3-sum on C9. Then the 6-sum on top right box, which must be 1+2+3. The 4-sum on C1 is also solved.
Some general strategy is mostly to consider the possible numbers on a cage to get some sure possibilities (e.g., must be 5+7 instead of 4+8), and to consider that total sum in a 3x3 box is 45 (e.g., the mid right box, being covered with all sums, helped to deduce the 22-cage should have a sum of 13 in that box, so can put 9 in R6C6).
The longest stuck point was resolving the 20-cage on R3. Eventually I figured that it's either 4 or 9 in R4C1, but dunno which. But figured that 4 will lead to a 7+9 in the remaining two spots, which leaves only 4 as the valid candidate on both R3C6 and R3C7, a contradiction. After getting past that, it's easy again.
