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Friends Of Appropriate Ages

There are n persons on a social media website.

There are n persons on a social media website. You are given an integer array ages where ages[i] is the age of the ith person.

A Person x will not send a friend request to a person y (x != y) if any of the following conditions is true:

Otherwise, x will send a friend request to y.

Note that if x sends a request to y, y will not necessarily send a request to x. Also, a person will not send a friend request to themself.

Return the total number of friend requests made.

Friends Of Appropriate Ages diagram

Example 1

Input: ages = [16,16]

Output: 2

Explanation: 2 people friend request each other.

Example 2

Input: ages = [16,17,18]

Output: 2

Explanation: Friend requests are made 17 -> 16, 18 -> 17.

Example 3

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

Output: 3

Explanation: Friend requests are made 110 -> 100, 120 -> 110, 120 -> 100.

Constraints

  • n == ages.length
  • 1 <= n <= 2 * 10^4
  • 1 <= ages[i] <= 120

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