First, I labeled the blocks starting in the top left corner, running down columns before hitting the next row.

4->5, 1->4, 2->1, 6->5, 4->5, 10->8, 11->10, 9->10, 7->9, 8->7, 10->8, 9->10, 10->11, 7->9, 8->10, 5->6, 8->7, 6->8, 8->10