# You are given a list of preferences for n friends, where n is always even. For each person i, preferences[i] contains a list of friends sorted in the order of preference. Friends in each list are denoted

Problem 2. [Category: Optional: Coding] Here is another problem that is relate to stable matching.
You are given a list of preferences for n friends, where n is always even. For each person i, preferences[i] contains a list of friends sorted in the order of preference. Friends in each list are denoted by integers from 0 to n – 1.
All the friends are divided into pairs. The pairings are given in a list pairs, where pairs[i] = [x,y;] denotes I is paired with y; and y, is paired with . However, this pairing may cause some of the friends to be unhappy. A friend is unhappy if x is paired
with y and there exists a friend a who is paired with b but:
a prefers a over y, and a prefers a over b. Return the number of unhappy friends.
Example 1:
1
Input: n = 4, preferences = [[1, 2, 3], [3, 2, 0], [3, 1, 0], [1, 2, 0]], pairs = [[0, 1], [2, 3]]
Output: 2
Explanation:
Friend 1 is unhappy because: – 1 is paired with 0 but prefers 3 over 0, and 3 prefers 1 over 2. Friend 3 is unhappy because: – 3 is paired with 2 but prefers 1 over 2, and 1 prefers 3 over 0. Friends 0 and 2 are happy. Example 2:
Input: n = 2, preferences = [[1], [0]], pairs = [[1, 0]]
Output: 0
Explanation: Both friends 0 and 1 are happy.
Example 3:
Input: n = 4, preferences = [[1, 3, 2], [2, 3, 0], [1, 3, 0], [0, 2, 1]], pairs = [[1, 3], [0,2]]
Output: 4
Please submit a script including test cases (examples included above or more) and instructions how to run the script.
[20 points]