Keep duplicate dates in a second dictionary
![A repeated date sets duplicates[date]=True. A third person on the same date does not create a second copy of that key.](/images/computational-thinking/week-7/duplicate-dates.png)
birthdays = {}
duplicates = {}
foreach X in scores {
dob = normalizedDayMonth(X.DateOfBirth)
if (isKey(birthdays,dob)) {
duplicates[dob] = True
}
else {
birthdays[dob] = True
}
}birthdays remembers every observed birthday; duplicates remembers only dates seen at least twice. Both are dictionaries of True flags. Repeated assignment duplicates[dob]=True leaves one entry for that date. It does not count occurrences or remember students.
For a constructed group of three people with the same birthday, duplicates still has one date key, but there are three unordered student pairs. A date group of size r contains r(r−1)/2 such pairs. Do not use the number of duplicate-date keys as the pair count.
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After one occurrence, is its date in duplicates?
Show explained answer
No. The second occurrence creates the duplicate-date flag.
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Three records share 1 Jan. How many duplicate-date keys and matching pairs?
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One duplicate-date key and three unordered pairs.
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Do True flags identify the students?
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No. Store IDs in the birthday values when you need to know who shares the date.