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MODULE NEIGHBOURS
IMPLICIT NONE
CONTAINS
LOGICAL FUNCTION FIND_NEIGHBOUR(MATRIX,FROM,TO)
INTEGER(KIND=SELECTED_INT_KIND(2)),DIMENSION(6,9),INTENT(IN)::MATRIX
INTEGER(KIND=SELECTED_INT_KIND(2)),INTENT(IN)::FROM,TO
INTEGER::I,J,K,L
FIND_NEIGHBOUR=.false.
WRITE(*,*) ' Can target be reached in one step?'
WRITE(*,2000) FROM,TO
2000 FORMAT(' Looking for way from ',I3,' to ',I3)
DO I=1,6
DO J=1,9
IF (MATRIX(I,J)==FROM) THEN
WRITE(*,*) 'Found our current position!'
DO K=-1,1
IF (I+K<1 .or. I+K>6) CYCLE
DO L=-1,1
IF (J+L<1 .or. J+L>9) CYCLE
IF (MATRIX(I+K,J+L)==TO) THEN
FIND_NEIGHBOUR=.true.
WRITE(*,*) ' Found the target!'
GOTO 10
END IF
END DO
END DO
END IF
END DO
END DO
WRITE(*,*) ' Did not find the target. Continue.'
WRITE(*,*) ''
10 CONTINUE
END FUNCTION FIND_NEIGHBOUR

SUBROUTINE SET_NEIGHBOURS(MATRIX,FROM,TO,WHERE,CHANGED)
INTEGER(KIND=SELECTED_INT_KIND(2)),DIMENSION(6,9),INTENT(INOUT)::MATRIX
INTEGER(KIND=SELECTED_INT_KIND(2)),INTENT(IN)::FROM,TO,WHERE
LOGICAL,INTENT(OUT)::CHANGED
INTEGER::I,J,K,L
CHANGED=.FALSE.
WRITE(*,*) ' Mark all clear fields from our current positions.'
DO I=1,6
DO J=1,9
IF (MATRIX(I,J)==FROM) THEN
DO K=-1,1
IF (I+K<1 .or. I+K>6) CYCLE
DO L=-1,1
IF (J+L<1 .or. J+L>9) CYCLE
IF (MATRIX(I+K,J+L)==WHERE) THEN
CHANGED=.TRUE.
MATRIX(I+K,J+L)=TO
END IF
END DO
END DO
END IF
END DO
END DO
10 CONTINUE
END SUBROUTINE SET_NEIGHBOURS
END MODULE NEIGHBOURS

PROGRAM LABYRINTH
USE NEIGHBOURS
IMPLICIT NONE
INTEGER(KIND=SELECTED_INT_KIND(2)),DIMENSION(6,9)::MATRIX=1
INTEGER(KIND=SELECTED_INT_KIND(2))::FROM=-2,TO=1,I,WHERE=0,TARGET=-3
CHARACTER,DIMENSION(6,9)::MATMAP
LOGICAL::CHANGED=.TRUE.
INTEGER::J

WRITE(*,*) 'Reading labyrinth...'
CALL GET_MATRIX(MATRIX)

WRITE(*,*) 'Finding path...'
WRITE(*,2003) TO
DO WHILE (.NOT. FIND_NEIGHBOUR(MATRIX,FROM,TARGET) .AND. TO<32)
WRITE(*,2003) TO
CALL SET_NEIGHBOURS(MATRIX,FROM,TO,WHERE,CHANGED)
IF (.NOT. CHANGED) GOTO 30
FROM=TO
TO=TO+1
WRITE(*,*) ''
CALL TO_MAP(MATRIX,MATMAP)
WRITE(*,2000) (MATRIX(I,1:9),I=1,6)
2000 FORMAT(9(2X,I3))
1000 FORMAT(9(A1))
WRITE(*,*) ''
END DO

2003 FORMAT(' At step ',I5)

WRITE(*,2001) TO
2001 FORMAT(' This labyrinth takes at least ',I2,' steps to traverse.')

WRITE(*,2000) (MATRIX(I,1:9),I=1,6)

STOP

WRITE(*,2000) (MATRIX(I,1:9),I=1,6)

30 WRITE(*,2002) FROM
2002 FORMAT(' This labyrinth cannot be traversed! Dead end at ',I2)
STOP
END PROGRAM LABYRINTH

SUBROUTINE GET_MATRIX(MATRIX)
INTEGER(KIND=SELECTED_INT_KIND(2)),DIMENSION(6,9),INTENT(OUT)::MATRIX
CHARACTER,DIMENSION(6,9)::MATMAP
INTEGER::I,J
WRITE(*,*) ''
READ(*,1000) (MATMAP(I,1:9),I=1,6)
WRITE(*,1000) (MATMAP(I,1:9),I=1,6)
WRITE(*,*) ''
WRITE(*,*) 'Converting labyrinth to int...'
WRITE(*,*) ''
1000 FORMAT(9(A1))
DO I=1,6
DO J=1,9
CALL CONVERT_CHAR(MATMAP(I,J),MATRIX(I,J))
END DO
END DO
WRITE(*,*) ''
WRITE(*,2000) (MATRIX(I,1:9),I=1,6)
2000 FORMAT(9(2X,I3))
WRITE(*,*) ''
END SUBROUTINE GET_MATRIX

SUBROUTINE CONVERT_CHAR(CHARA,INT)
CHARACTER,INTENT(IN)::CHARA
INTEGER(KIND=SELECTED_INT_KIND(2)),INTENT(OUT)::INT
!WRITE(*,*) CHARA
IF (CHARA=='#') INT=-1
IF (CHARA=='.') INT=0
IF (CHARA=='<') INT=-2
IF (CHARA=='>') INT=-3
END SUBROUTINE CONVERT_CHAR

Can target be reached in one step?
Looking for way from 12 to -3
Found our current position!
Found the target!
This labyrinth takes at least 13 steps to traverse.
-1 -2 -1 -1 -1 -1 11 -1 -1
-1 1 1 -1 -3 12 -1 10 10
-1 -1 2 -1 -1 -1 -1 9 -1
-1 3 -1 -1 8 8 8 -1 -1
-1 -1 4 -1 -1 7 -1 -1 -1
-1 -1 5 5 6 7 -1 -1 -1

10 CONTINUE
I+I=1
IF (I<100) GOTO 10