Two-Dots is NP-Hard

Instance of Exact Cover by 3-Sets
One set per row, elements are separated by spaces. The elements must be the integers in {1, 2, ..., 3k} for some positive odd integer k.
Click and drag to make a move.
2 5 7 1 4 5 2 6 8 1 3 8 4 6 9
Generate!

Remaining moves: 0       Goal: 0/0       0/0