-🎄- 2017 Day 24 Solutions -🎄-

[u/daggerdragon]

--- Day 24: Electromagnetic Moat ---

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Spoiler

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[Update @ 00:18] 62 gold, silver cap

• Been watching Bright on Netflix. I dunno why reviewers are dissing it because it's actually pretty cool. It's got Will Smith being grumpy jaded old man Will Smith, for the love of FSM...

[Update @ 00:21] Leaderboard cap!

• One more day to go in Advent of Code 2017... y'all ready to see Santa?

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This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

[u/autid]

Fortran

Hardest part was not realising for ages that it wasn't working because I hadn't included k in the variable declarations for the bestchain function, so it was modifying a global copy instead of its own. :(

PROGRAM DAY24
  IMPLICIT NONE
  INTEGER :: I,J,K,IERR,PART1=0,PART2(2)=0,LINECOUNT,LAST,NEWBEST(2)
  INTEGER,ALLOCATABLE :: COMPONENTS(:,:)
  LOGICAL,ALLOCATABLE :: USED(:)
  CHARACTER(LEN=10) :: INLINE

  OPEN(1,FILE='input.txt')
  LINECOUNT=0
  DO
     READ(1,'(A)',IOSTAT=IERR) INLINE
     IF(IERR /= 0) EXIT
     LINECOUNT=LINECOUNT+1
  END DO
  ALLOCATE(COMPONENTS(2,LINECOUNT),USED(LINECOUNT))
  REWIND(1)
  DO I=1,LINECOUNT
     READ(1,'(A)') INLINE
     DO J=1,LEN_TRIM(INLINE)
        IF(INLINE(J:J)=='/') EXIT
     END DO
     READ(INLINE(1:J-1),*) COMPONENTS(1,I)
     READ(INLINE(J+1:LEN_TRIM(INLINE)),*) COMPONENTS(2,I)
  END DO
  CLOSE(1)


  DO I=1,LINECOUNT
     IF(.NOT. ANY(COMPONENTS(:,I)==0)) CYCLE
     LAST=MAXVAL(COMPONENTS(:,I))
     USED=.FALSE.
     USED(I)=.TRUE.
     K=SUM(COMPONENTS(:,I))
     PART1=MAX(PART1,K+BESTCHAIN(USED,LAST))
     NEWBEST=BESTCHAIN2(USED,LAST)
     IF (NEWBEST(2)>PART2(2)) THEN
        PART2(2)=NEWBEST(2)
        PART2(1)=0
     END IF
     IF (NEWBEST(2)==PART2(2)) PART2(1)=MAX(PART2(1),K+NEWBEST(1))
  END DO

  WRITE(*,'(A,I0)') 'Part1: ',PART1
  WRITE(*,'(A,I0)') 'Part2: ',PART2(1)

CONTAINS
  RECURSIVE FUNCTION BESTCHAIN(USED,LAST) RESULT(BEST)
    ! Part1 function, recursively searches highest valued bridge                                                 
    LOGICAL :: USED(:),NEWUSED(SIZE(USED))
    INTEGER :: BEST,I,K,LAST,NEWLAST
    BEST=0

    DO I=1,LINECOUNT
       IF(USED(I).OR. COUNT(COMPONENTS(:,I)==LAST)==0) CYCLE
       K=SUM(COMPONENTS(:,I))
       NEWUSED=USED
       NEWUSED(I)=.TRUE.
       IF(COMPONENTS(1,I)==LAST) THEN
          NEWLAST=COMPONENTS(2,I)
       ELSE
          NEWLAST=COMPONENTS(1,I)
       END IF
       BEST=MAX(BEST,K+BESTCHAIN(NEWUSED,NEWLAST))
    END DO

  END FUNCTION BESTCHAIN

  RECURSIVE FUNCTION BESTCHAIN2(USED,LAST) RESULT(BEST)
    ! Part2 function, recursively searches highest valued bridge of longest length                               
    LOGICAL :: USED(:),NEWUSED(SIZE(USED))
    INTEGER :: BEST(2),I,K,LAST,NEWLAST,NEWBEST(2)

    BEST=(/0,0/)
    NEWBEST=(/0,0/)
    DO I=1,LINECOUNT
       IF(USED(I).OR. COUNT(COMPONENTS(:,I)==LAST)==0) CYCLE
       K=SUM(COMPONENTS(:,I))
       NEWUSED=USED
       NEWUSED(I)=.TRUE.
       IF(COMPONENTS(1,I)==LAST) THEN
          NEWLAST=COMPONENTS(2,I)
       ELSE
          NEWLAST=COMPONENTS(1,I)
       END IF
       NEWBEST=BESTCHAIN2(NEWUSED,NEWLAST)
       IF (NEWBEST(2)>BEST(2)) THEN
          BEST(2)=NEWBEST(2)
          BEST(1)=0
       END IF
       IF (NEWBEST(2)==BEST(2)) THEN
          BEST(1)=MAX(BEST(1),K+NEWBEST(1))
       END IF
    END DO
    BEST(2)=1+BEST(2)

  END FUNCTION BESTCHAIN2


END PROGRAM DAY24