
May 21 hard solving guide
I posted the strategies and notation helper here.
Wow, this is hard.
As usual for puzzles like these we use a chessboard notation, A1 is a discard, F1 is a 5, A5 is a 0, F5 is also a 5.
Puzzles like these can be arena driven where we look at a tile and the available dominos and find only one domino can go on that tile or domino driven where we look at a domino and find it has only one place where it can go. This solution is 100% arena driven.
Major breakpoints where you could stop and enjoy figuring it out is after step 1, step 4, step 5. Step 2-4 is really one step I just broke it down for easier understanding. Step 5 is independent of the previous steps, it could be done earlier. Many orders are possible for the placement itself, the before section is the hard one.
Before placement >!except one!<:
- >!E1 can't go up as that'd be 1-1 so it goes left or right, either way the 1-5 is here.!<
- >!A3 can't go right as that'd be the 2-2.!<
- >!Let's presume A3 goes up, it's the 2-4. B4 goes right as well because down or up would be the same 2-4. Also A5 goes right. Now C5 is forced to the right which is the 1-5 but that's booked.!<
- >!So A3 goes down, it's the 2-0.!<
- >!There are five halves for each number, count the tiles on the board for each, three 3s and a 5 is missing. At most two 3s fit in the discard so one is in the 2c= that means the 2c= is 3s. The third 3 is in the discard, the other discard is a 5.!<
Placement:
- >!A4 goes up, 4-0: right? 4-4, doesn't exist.!<
- >!A1-B1 is 3-5.!<
- >!F5 goes left, 5-4: down? 5-3, used.!<
- >!D5 goes down, 5-0: left? 5-1, booked.!<
- >!F4 goes down, 3-0: left? 3-3, doesn't exist. (But also F3 goes up: left? 0-4. Down? 0-2. Both are used.)!<
- >!E4-E3 is 3-4.!<
- >!C4 goes up, 3-1: left? 3-4, down? 3-0. Both are used.!<
- >!B4-B5 is 4-2.!<
- >!B3 goes down, 2-3: right? 2-0, used.!<
- >!C3 goes right, 0-1: down? 0-2, used.!<
- >!C2 goes down, 2-1: right? 2-4, used.!<
- >!Place 4-1, 2-5 and the 1-5 last.!<
Note: >!the only place for 5-2 is on F1-F2 and so E1 goes left meaning the 5-1 is on D1-E1 from the very beginning but we didn't need to figure this out, it's enough the 5-1 is booked.!<
Also note >!you can't avoid solving the upper left corner because you can fill the board almost https://i.imgur.com/BxGrsVY.png with the only problem being A5 and B3 are not being next to each other so you won't find any other contradiction!<