## Editorial for Mock CCC '23 Contest 1 J3 - Pairing Gifts

Remember to use this editorial

**only**when stuck, and**not to copy-paste code from it**. Please be respectful to the problem author and editorialist.**Submitting an official solution before solving the problem yourself is a bannable offence.**Author:

For this problem, we need to count the number of pairs such that and .

#### Subtask 1

Subtask 1 is created to reward full solutions that incorrectly handle the condition.

#### Subtask 2

Firstly, observe that since all are distinct and all are distinct, each can only have one that forms a valid bundle. For this subtask, we can loop through all for each and check if there exists a pair that satisfies the conditions provided.

**Time Complexity:**

#### Subtask 3

For full marks, the look-up for must be made more efficient. We can maintain a map that maps the value of each gift in to its index. Then for each , we can check if there exists a with value at a valid index.

**Time Complexity:** or

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