How should I practice Count Centaur Friend Requests?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Meta phone screen problems in FastPrep.

Is Count Centaur Friend Requests associated with Meta?

FastPrep tags this as a Meta phone screen coding practice problem when the problem catalog has that company and stage context.

Count Centaur Friend Requests

Meta● MediumINTERNPHONE SCREEN

Learn

Problem statement

A group of centaurs sign up for accounts and may send directed friend requests to one another. You are given their integer ages in ages.

A centaur with age x sends a request to a different centaur with age y only when all of these rules hold:

y >= x / 2 + 7, where the division is real-number division.
y <= x.
If x > 100, then y >= 100.

Count the total number of directed friend requests. Centaurs with the same age are still distinct people, and no centaur may send a request to themself.

Function

countCentaurFriendRequests(ages: int[]) → long

Examples

Example 1

ages = [120,110]return = 1

The 120-year-old centaur sends one request to the 110-year-old centaur. The reverse request is disallowed because the recipient would be older.

Example 2

ages = [120,110,99]return = 1

The 99-year-old recipient is disallowed for both senders over 100, so only the request from age 120 to age 110 is sent.

Example 3

ages = [120,45,230,400,88,300,101]return = 4

Exactly four ordered sender-recipient pairs satisfy every age rule.

Example 4

ages = [101,120,230,400,88,45,55,300]return = 6

Counting valid ordered pairs across all eight distinct centaurs gives six requests.

Example 5

ages = [100,110,120]return = 3

The valid requests are from age 110 to 100 and from age 120 to both 100 and 110.

Constraints

1 <= ages.length <= 2 * 10^5.
1 <= ages[i] <= 10^9.
Each position in ages represents a distinct centaur.