I've no idea what's obvious and what isn't in sudoku solving, but have you managed to train your brain to see/hear 51492 and INSTANTLY respond with 3678? It speeds things up no end if you can look at what's present and immediately know what's missing.ronaldx wrote:How do people solve Killer Sudoku so quickly? They make my brain ache, for me I did that one relatively fluently and still ended up way down the list.

Specific to solving killers: there are certain cages which DEFINITELY contain a specific set of numbers, much as in kakuro - if you see a two-cell 3 interacting with a two-cell 4, for example, you're likely going to be able to fill one of those two cages with definites straight away. A two-cell 3 all in the same row with a two-cell 7 tells you the contents of both cages.

The 'one row sums to 45, two rows sum to 90' so looking for cages that exactly fill every cell bar one/every cell plus one is helpful for more complex Killers, but tends to be an unnecessarily slow step in the croco-killers I've seen so far. When that technique IS useful though, it's quicker to do the sums modulo 10; if you're only looking for the content of one cell, you already know that you're looking for a one-digit number.