SECTION 13 / 31
Store the IDs who share each birthday
birthdays = {}
duplicates = {}
foreach X in scores {
dob = normalizedDayMonth(X.DateOfBirth)
id = X.CardNo
if (isKey(birthdays,dob)) {
duplicates[dob] = True
birthdays[dob] = birthdays[dob] ++ [id]
}
else {
birthdays[dob] = [id]
}
}
foreach dob in keys(duplicates) {
sharedIDs = birthdays[dob]
}On Aditya’s card, birthdays[15 Mar] becomes [7]. On Monika’s card it becomes [7,21]. Here length(birthdays[15 Mar]) is 2, while length(keys(birthdays)) is 29 after the full scan. One counts students at a chosen date; the other counts observed dates.
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Why append [id] rather than id?
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++ concatenates lists, so wrap the new ID in a one-element list.
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Does birthdays[dob]=[id] on every card retain all students?
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No. It replaces earlier lists. Append on existing keys.
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What does birthdays[15 Mar] return here?
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The whole ID list [7,21], not one ID and not just a Boolean flag.