day1-2.p

/*
--- Part Two ---

You notice a progress bar that jumps to 50% completion. Apparently, the door isn't yet satisfied, but it did emit a star as encouragement. The instructions change:

Now, instead of considering the next digit, it wants you to consider the digit halfway around the circular list. That is, if your list contains 10 items, only include a digit in your sum if the digit 10/2 = 5 steps forward matches it. Fortunately, your list has an even number of elements.

For example:

    1212 produces 6: the list contains 4 items, and all four digits match the digit 2 items ahead.
    1221 produces 0, because every comparison is between a 1 and a 2.
    123425 produces 4, because both 2s match each other, but no other digit has a match.
    123123 produces 12.
    12131415 produces 4.

What is the solution to your new captcha?
*/
DEFINE VARIABLE cInput AS CHARACTER INITIAL "61697637962276641366442297247367117738114719863473648131982449728688116728695866572989524473392982963976411147683588415878214189996163533584547175794158118148724298832798898333399786561459152644144669959887341481968319172987357989785791366732849932788343772112176614723858474959919713855398876956427631354172668133549845585632211935573662181331613137869866693259374322169811683635325321597242889358147123358117774914653787371368574784376721652181792371635288376729784967526824915192526744935187989571347746222113625577963476141923187534658445615596987614385911513939292257263723518774888174635963254624769684533531443745729344341973746469326838186248448483587477563285867499956446218775232374383433921835993136463383628861115573142854358943291148766299653633195582135934544964657663198387794442443531964615169655243652696782443394639169687847463721585527947839992182415393199964893658322757634675274422993237955354185194868638454891442893935694454324235968155913963282642649968153284626154111478389914316765783434365458352785868895582488312334931317935669453447478936938533669921165437373741448378477391812779971528975478298688754939216421429251727555596481943322266289527996672856387648674166997731342558986575258793261986817177487197512282162964167151259485744835854547513341322647732662443512251886771887651614177679229984271191292374755915457372775856178539965131319568278252326242615151412772254257847413799811417287481321745372879513766235745347872632946776538173667371228977212143996391617974367923439923774388523845589769341351167311398787797583543434725374343611724379399566197432154146881344528319826434554239373666962546271299717743591225567564655511353255197516515213963862383762258959957474789718564758843367325794589886852413314713698911855183778978722558742329429867239261464773646389484318446574375323674136638452173815176732385468675215264736786242866295648997365412637499692817747937982628518926381939279935993712418938567488289246779458432179335139731952167527521377546376518126276"  NO-UNDO.
/* DEFINE VARIABLE cInput AS CHARACTER INITIAL "123123"  NO-UNDO. */
DEFINE VARIABLE cChar AS CHARACTER   NO-UNDO.
DEFINE VARIABLE cNextChar AS CHARACTER   NO-UNDO.
DEFINE VARIABLE i AS INTEGER     NO-UNDO.
DEFINE VARIABLE iSum AS INTEGER     NO-UNDO.
DEFINE VARIABLE iLength AS INTEGER     NO-UNDO.
DEFINE VARIABLE iNextPos AS INTEGER     NO-UNDO.

iLength = LENGTH(cInput) / 2.

DO i = 1 TO LENGTH(cInput):
    cChar = SUBSTRING(cInput, i, 1).
    iNextPos = (i + iLength) MODULO (2 * iLength).
    IF iNextPos = 0 THEN iNextPos = 2 * iLength.
    cNextChar = SUBSTRING(cInput, iNextPos, 1).
    IF cChar = cNextChar THEN
        iSum = iSum + INTEGER(cNextChar).
END.

MESSAGE iSum
    VIEW-AS ALERT-BOX INFO BUTTONS OK.