Find the Celebrity

celebrity_finder.py

"""
Description:
Suppose you are at a party with n people (labeled from 0 to n - 1) and among them,
there may exist one celebrity. The definition of a celebrity is that all the other
n - 1 people know him/her but he/she does not know any of them.
Now you want to find out who the celebrity is or verify that there is not one. The only
thing you are allowed to do is to ask questions like: "Hi, A. Do you know B?" to get
information of whether A knows B. You need to find out the celebrity (or verify there
is not one) by asking as few questions as possible (in the asymptotic sense).

Given API, bool knows(a, b), which tells you whether A knows B. Implement a function
int findCelebrity(n), your function should minimize the number of calls to knows. There
will be exactly one celebrity if he/she is in the party. Return the celebrity's label
if there is a celebrity in the party. If there is no celebrity, return -1.
"""

###
# API
# def knows(a, b):
#   """
#   returns True if a knows b, False otherwise
#   :type a: int
#   :type b: int
#   :rtype: bool
#   """
###

class CelebrityFinder:
    def findCelebrity(self, n):
        """
        :type n: int
        :rtype: int
        """
        celeb = 0
        for i in range(1, n):
            if knows(celeb, i):
                celeb = i
        # verify
        for i in range(celeb):
            if knows(celeb, i):
                return -1
        # verify 2
        for i in range(n):
            if i == celeb:
                continue
            if not knows(i, celeb):
                return -1
        return celeb