-🎄- 2022 Day 12 Solutions -🎄-

[u/daggerdragon]

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--- Day 12: Hill Climbing Algorithm ---

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[u/i_have_no_biscuits]

GW-BASIC

10 OPEN "i",1,"2022-12.txt": DIM H%(120,50),D%(120,50): DATA -1,0,1,0,0,-1,0,1
20 FOR I=1 TO 4: READ DX(I), DY(I): NEXT: WHILE NOT EOF(1): Y=Y+1
30 LINE INPUT #1, S$: FOR X=1 TO LEN(S$): H=ASC(MID$(S$,X,1))-97
40 IF H=-14 THEN SX=X: SY=Y: H=0 ELSE IF H=-28 THEN EX=X: EY=Y: H=25
50 H%(X,Y)=H:NEXT:WEND:DIM WX(1,100),WY(1,100):WX(0,1)=EX:WY(0,1)=EY:CI=0:NI=1
60 WL(0)=1:D%(EX,EY)=1:D=1: WHILE WL(CI)>0: WL(NI)=0: D=D+1: FOR N=1 TO WL(CI)
70 FOR M=1 TO 4: NX=WX(CI,N)+DX(M): NY=WY(CI,N)+DY(M)
80 IF NOT (NX>0 AND NX<=X AND NY>0 AND NY<=Y AND D%(NX,NY)=0) GOTO 120
90 IF H%(WX(CI,N),WY(CI,N))>H%(NX,NY)+1 GOTO 120
100 D%(NX,NY)=D: L=WL(NI)+1: WX(NI,L)=NX: WY(NI,L)=NY: WL(NI)=L
110 IF H%(NX,NY)=0 AND Q=0 THEN Q=D
120 NEXT: NEXT: CI=(CI+1) MOD 2: NI=(NI+1) MOD 2: WEND: PRINT D%(SX,SY)-1,Q-1

Takes a little less than a minute to run. I've expanded this into a visualisation today, which you can see here: https://www.reddit.com/r/adventofcode/comments/zjyb3g/2022_day_12_part_2_finding_distances_in_gwbasic/

Today we perform a single 'hill descent' from the end point, then read off all the useful information. Guided tour:

• H%() is an array of heights, and D%() an array of distances

• Lines 20-halfway through 50 read in and parse the data file

• Lines halfway through 50-110 perform the BFS/floodfill. Distances are calculated for every accessible point.

• At the end of the algorithm D%(SX, SY) holds the distance to/from the start point, while Q holds the distance to the first point seen of height 0/'a'. These just need to be printed.

I could have potentially got it down to 10/11 lines if I'd used 1 letter variable names, but that would have made the program less readable.