3. Fraudulent Accounts A large online social networking company has recently dis
ID: 3596616 • Letter: 3
Question
3. Fraudulent Accounts A large online social networking company has recently discovered that it may have a problem with a number of accounts that are spreading false information through 3-1 the site. The company has a collection of n accounts that they've been monitoring over the last several months, suspecting them of being used for such activity. Eaclh account has the following data associated with it: a user id, some possibly fraudulent information (such as the name, etc.), and a unique encrypted number generated by the site when the account was created. A user can have more than one account on the site The company will not disclose the identity of the account holders directly without a subpoena, but will tell if two accounts belong to the same user. The government agency's question is the following: among the collection of n accounts is there a set of more than n/2 of them that are all associated with the same user? Assume that the only feasible operation the government investigators can do with the accounts is to choose two of them and ask the company if they belong to the same user (and the company people get more and more reluctant to answer each time). Show how to decide the answer to the agency's question with only O(n logn) requests to the social networking company.Explanation / Answer
The social net working site issued accounts to their users with their user id and name soem other details.
User id is unique for each dataset.
Company found false information over some accounts.
Assume company have n accounts each account has an unique ID for identification.
If the user has moe than one account there is a possibility fro each user has 2 accounts
so there is chance to duplication of data any where in the collectd information except the user ID.
Each user id and associated data are compared to similar data whichis earesr or nearer data.
Here is the time complexity is one of the key point to sort out these.
Time complexity is commonly estimated by counting the number of elementary operations performed by the algorithm, where an elementary operation takes a fixed amount of time to perform. Thus, the amount of time taken and the number of elementary operations performed by the algorithm differ by at most a constant factor.
if that simple algorithm is given a list of length n (the variable traditionally used for such things), then it will use that operation n times.
Each user request has only associated with O(n log n) means, a fastest comparision has done here to find ooddan out.
So each user compared with all others , n-1 comparisons are take palce here.
this will be done for all n accounts in the site.
so totally n * n-1 *......... comparisions for alla counts in the site.
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