Shortening this Code to process nested tuple even further without the use of max()

Question

I have the code:

marks = tuple(tuple((input("Enter subject: "), input("Enter marks: "))) for _ in range(int(input("Enter number of tuples: "))))
print(tuple((s[:3].upper(), max(int(m) for t, m in marks if t == s)) for s in set(t for t, m in marks)))

#INPUT
(("Physics",131),("Chemistry",30),("Physics",100),("Computers",50),("Chemistry",20))
#OUTPUT
(('COM', 50), ('PHY', 131), ('CHE', 30))

As you can see, the output is a nested tuple of the first three capitalized letters of the subject and the maximum mark given for each subject.

You can assume that Physics, Chemistry and Computers are the only subjects that the user inputs, and that they always use the same spelling for the subjects.

The order of the subjects in the output does not matter.

Is there anyway I can do the same without using the max function? The length of the code should optimally be at 2 lines or if at all possible, a single line. The maximum limit of the number of lines of code is 3.

The solution should try to contain no built in functions if possible. Functions like sort(), sorted() and max() are strictly not allowed.

Answer 1

1 line, 180 173 171 bytes

7 bytes saved thanks to Jonathan Allen

exec("x={}\n"+"if x.get(a:=input('Enter subject: ')[:3].upper(),b:=int(input('Enter marks: ')))<=b:x[a]=b\n"*int(input("Enter number of tuples: "))+"print((*x.items(),))")

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3 lines, 171 163 160 bytes

8 bytes saved thanks to Jonathan Allen

x,i,e={},input,'Enter '
exec("if x.get(a:=i(e+'subject: ')[:3].upper(),b:=int(i(e+'marks: ')))<=b:x[a]=b\n"*int(i(e+"number of tuples: ")))
print((*x.items(),))

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Here's another approach that yields fewer bytes. It can be done in 1, 2 or 3 lines, with more lines enabling shorter overall programs. There's probably still even some improvements to be made here.

Answer 2

Python, 204 188 bytes

-16 bytes thanks to @WheatWizard

m=[*((input("Enter subject: "),int(input("Enter marks: ")))for _ in'*'*int(input("Enter number of tuples: ")))]
print((*((i[:3].upper(),j)for i,j in m if all(y!=i or z<=j for y,z in m)),))

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Python, 212 bytes

1 line

print((*[m:=[*((input("Enter subject: "),int(input("Enter marks: ")))for _ in range(int(input("Enter number of tuples: "))))]][:0],*((i[0][:3].upper(),i[1])for i in m if all(z[0]!=i[0]or z[1]<=i[1]for z in m)),))

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These are just some trivial golfs on your approach. It could probably be made much shorter. If there are ties this will print both.