Dictionary Solution

# Enter your code here. Read input from STDIN. Print output to STDOUT
n = int(input())

rooms = list(map(int,input().split()))

# print(n)
counts = {}
for _ in rooms:
    counts[_] = counts.get(_,0)+1
print(min(counts,key=counts.get))

from collections import Counter
k=int(input())
rn=input().split()
l=dict(Counter(rn))
for k,v in l.items():
        if v==1:print(int(k))

Enter your code here. Read input from STDIN. Print output to STDOUT

k=int(input()) list_k=list(map(int,input().split()))

Use set to get the unique value in the list

room_set = set(list_k)

now we are multiplying sum of the set with k first

then we are subtracting it with the original list's sum (so that only the captains value*(k-1) remains)

then we are dividing by (k-1) to get the actual value

captain_room = (sum(room_set)*k - sum(list_k)) // (k-1)

print(captain_room)

For Python3 Platform

k = int(input())
room_numbers = input().split()
unique_room_numbers = set(room_numbers)

for num in unique_room_numbers:
    room_numbers.remove(num)
    
    if(num not in room_numbers):
        print(int(num))
        break

How does this fail only Test Case 1?!

from collections import Counter

K = int(input())
rooms = list(Counter(map(int,input().split())))

print(rooms[-1])