Logic Masters Deutschland e.V.

• Tridoku: Place the digits 1-9 once each in every outlined region, each side of the large yellow triangle, each side of the small blue triangle, and the disconnected red region. Green cells are in both the yellow and blue triangles. Two of the same digit may not touch each other, even at a point.
• X-Sums: A number outside of the puzzle represents the sum of the digits in the first X cells seen from the clue, where X is the digit in the cell closest to the clue. X-sums are counted in a straight line from the starting cell, moving along rows of cells that share edges. X-sum clues must be valid in both rows that begin at the starting cell.

Note how the X-Sums work in this example image. The first 5 digits in each direction from the clue each sum to 17, and unlike X-Sums in normal sudoku, it's possible to repeat digits within a sum in tridoku, as long as doing so does not violate another rule.

Solve in Penpa