Spoilers/Hints Corners sort easily, then 1 is in the middle of R1 and R20, then 1's diagonally (left and right) down from top and up from bottom. C6 blocks start R6 and R12, C16 blocks start R6 and R13, C11 blocks start at R5 and R13. Join them all up.
multiple answers possible -> bad.
Corners sort easily, then 1 is in the middle of R1 and R20, then 1's diagonally (left and right) down from top and up from bottom. C6 blocks start R6 and R12, C16 blocks start R6 and R13, C11 blocks start at R5 and R13. Join them all up.