Count friend requests based on age rules

Q: Count friend requests based on age rules

This question evaluates algorithmic problem-solving skills involving array processing, counting and combinatorics under conditional constraints and frequency handling.

Q: How do I approach Coding & Algorithms interview questions?

Coding & Algorithms questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master coding & algorithms interviews.

Question

Problem

You are given an array ages, where ages[i] is the age of the i-th person. A person of age A will send a friend request to a person of age B if all conditions hold:

$B > 0.5 \times A + 7$
$B \le A$

Each request is directed (A→B). A person cannot send a request to themselves.

Return the total number of friend requests that will be sent.

Input

ages : integer array

Output

An integer: total number of directed friend requests.

Constraints (you may assume typical interview bounds)

$1 \le n \le 2\times 10^4$
$1 \le ages[i] \le 120$

Examples

ages = [16, 16]

Each 16-year-old can request the other (since $16 > 0.5\cdot16 + 7 = 15$ and $16 \le 16$ )
Total = 2

ages = [20, 30, 100, 110, 120]

Compute total directed requests that satisfy the rules.