A Medium 11×11 Puzzle Solved with Shape Squeeze in 19 Steps

This 11×11 board rates as medium (difficulty score 835). Solving it from scratch takes 19 logical steps, using 7 techniques: Single cell, Row/column exclusion, Adjacency clear, Region confinement, Line confinement, Paired regions, Shape squeeze. Every step below is forced: nothing here is a guess.

1. First, every open cell left in this region sits in row 1, so its marker has to land there; that clears every other open cell in the row.
2. Next, place a marker at C2. Region has exactly one open cell left. Placing here clears the rest of row 2, column C, and its region. Placing here also clears its 2 touching neighbours.
3. Then, place a marker at K3. Region has exactly one open cell left. Placing here clears the rest of row 3, column K, and its region. Placing here also clears its 1 touching neighbour.
4. After that, place a marker at J1. Region has exactly one open cell left. Placing here clears the rest of row 1, column J, and its region.
5. Now, place a marker at I5. Region has exactly one open cell left. Placing here clears the rest of row 5, column I, and its region. Placing here also clears its 2 touching neighbours.
6. From there, together, two regions have open cells only in columns A and B; with one marker each, those two markers have to fill exactly those two columns, so every other region's open cells there can be cleared.
7. Following that, every open cell in row 11 belongs to the same region, so that region's marker has to be somewhere in this row; that clears every other open cell in the region.
8. First, every open cell in row 10 belongs to the same region, so that region's marker has to be somewhere in this row; that clears every other open cell in the region.
9. Next, every open cell in row 9 belongs to the same region, so that region's marker has to be somewhere in this row; that clears every other open cell in the region.
10. Then, every remaining candidate in this region touches B7, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
11. After that, place a marker at A7. Row 7 has exactly one open cell left. Placing here clears the rest of row 7, column A, and its region. Placing here also clears its 1 touching neighbour.
12. Now, place a marker at B4. Region has exactly one open cell left. Placing here clears the rest of row 4, column B, and its region.
13. From there, every open cell left in this region sits in row 6, so its marker has to land there; that clears every other open cell in the row.
14. Following that, every remaining candidate in this region touches E10, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
15. First, place a marker at D10. Region has exactly one open cell left. Placing here clears the rest of row 10, column D, and its region. Placing here also clears its 1 touching neighbour.
16. Next, place a marker at F9. Region has exactly one open cell left. Placing here clears the rest of row 9, column F, and its region. Placing here also clears its 1 touching neighbour.
17. Then, place a marker at E6. Region has exactly one open cell left.
18. After that, place a marker at H8. Region has exactly one open cell left. Placing here clears the rest of row 8, column H, and its region.
19. Finally, place a marker at G11. Region has exactly one open cell left.

The key move here was Shape squeeze. Once you can spot that, this board falls quickly. ∎