FB面经 解题指南 （持续更新）

277. Find the Celebrity

 

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 othern - 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).

You are given a helper function bool knows(a, b) which tells you whether A knows B. Implement a functionint findCelebrity(n), your function should minimize the number of calls toknows.

Note: 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.

 

这道题上了锁，没有测过。不过是一道经典的问题，传说中的社会名流问题，存在O(n)的算法。算法如下：

1. Pick up two people, A and B. If A knows B, A could not be the celebrity. Otherwise B cannot be the celebrity. Throw away the one that is not celebrity from the array.

2. Repeat Step 1 n-1 times. The last one that remains in the array is a candidate.

3. Verify the candidate.