SocialNetwork | Topcoder Archive

Problem Statement

A new social network automatically matches people together based upon a shared interest. A list of interests for each member of the social network is given in the String[] interests. Each element represents the interests of a single member: each character ('A'-'Z') represents a different interest. Two individuals become friends if they have at least one interest in common. Return the average number of friends each member has.

Definition

Class:: SocialNetwork
Method:: averageFriends
Parameters:: String[]
Returns:: double
Method signature:: double averageFriends(String[] interests)
(be sure your method is public)

Notes

Your return value must have an absolute or a relative error at most 10^(-9).

Constraints

interests will contain between 2 and 50 elements, inclusive.
Each character in each element of interests will be an uppercase English letter ('A'-'Z').
The characters in each element of interests will be distinct.

Examples

```
{"A", "A"}
```
```
Returns: 1.0
```
Two people who share a common interest. Thus, they each have one friend, and the average number of friends is therefore also 1.
```
{"ABC", "DE", "FGHIJ"}
```
```
Returns: 0.0
```
Three people with no common interests.
```
{"ABC", "DE", "FGHIJA"}
```
```
Returns: 0.6666666666666666
```
This is almost the same situation as Example #1 but now two of the people share a common interests. Now these three people have 1, 0, and 1 friends, respectively. The average number of friends is (1+0+1)/3 = 2/3 = 0.6666666667.
```
{"AB", "AC", "AD", "AE", "BCDE"}
```
```
Returns: 4.0
```
All of these people are friends with each other, even though there is no single topic they would all be interested in.
```
{"ABCDE", "BCDEF"}
```
```
Returns: 1.0
```
Even if people share multiple common interests, they are only friends once.
```
{"", "", "", ""}
```
```
Returns: 0.0
```
Four grumpy people who are not interested in anything.

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