Re: a challenge related to the 15 puzzle Don Shepherd Posting Freak Posts: 1,392 Threads: 142 Joined: Jun 2007 01-19-2011, 04:53 AM Well, the HP-32sii version takes a while to run because it has to decode registers A-D in which 4 numbers are stored in each register. I did that to avoid using so many registers. This version stores a single cell value in each register A-P. While it uses many more registers than the other version, it runs much quicker (about 7 seconds versus 40 seconds). Life (and programming) is all about trade-offs! ```Program to determine solvability of 15 puzzle for 32s. This one is faster than the one that stores 4 numbers in each register A-D. Register usage: A-P - 16 cell values, entered after XEQ A Q - number of inversions, including row number of empty cell R - current outer loop cell value i - indirect addressing and inner loop index T - outer loop index Usage: XEQ A enter 16 cell values (0 for empty cell) R/S after each program displays number of inversions; if even, puzzle is solvable Code: lbl a entry point 1.016 loop to get cell values sto i lbl b r/s enter each of 16 values sto (i) stores in A-P x<>0 if 0 calc row# goto c 3 rcl+i 4 / ip sto q inversion count starts with row# of empty cell lbl c isg i goto b 1.015 outer loop goes from 1 to 15 sto t outer loop index lbl d rcl t get current outer loop cell value sto i and store in R rcl (i) sto r rcl t ip 1.016 + inner loop goes from t+1 to 16 sto i inner loop index lbl e rcl (i) x=0 if inner loop cell value is 0, ignore goto f rcl r current outer loop cell value x

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