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Joining & Splitting Blocks
Level 3: Hard
Join two filled groups that must belong to the same block, or split them when joining would make a block too long.
There is only one block of 5, so the two filled cells at positions 2 and 5 must belong to it. Everything between them is filled.
Splitting is the opposite case: when joining two groups would exceed every clue that could cover them, they must be separate blocks and the cell between them is crossed out.