How to operate on nested dictionary in python 3.x?

Question

I am stuck with this question, can you solve the challenge? Here we go!

We represent scores of players across a sequence of matches in a two level dictionary as follows:

Answer 1

Some code golfing with functools.reduce:

from functools import reduce
from collections import Counter

v = reduce(lambda x, y: x.update(y) or x, d.values(), Counter()).most_common(1)[0])
print(v)
# ('player3', 100)