i:.'0:"i/22.in"
(⊻):{2/~=/+2\(x;y)}                     / vectorized bitwise xor
s:{16777216!x⊻_y*x}/[;(64;1%32;2048)]   / next secret number
+/*|p:2000s\i                           / part 1: sum of every buyer's 2000th secret number
k:+4(19/)':9+1_-':p:10!p                / hash each sequence of four price changes
|/+/k{@[&*/4#19;|x;:;|y]}'+4_p          / part 2: most bananas you can buy

For part 2, I ended up implementing a hashtable... I wish dicts were hashtables.

xor implementation stolen from shadow of course!

~/aoc24k/22.html