825. Friends Of Appropriate Ages
https://leetcode.com/problems/friends-of-appropriate-ages/
Some people will make friend requests. The list of their ages is given and
ages[i] is the age of the ith person. Person A will NOT friend request person B (B != A) if any of the following conditions are true:
age[B] <= 0.5 * age[A] + 7age[B] > age[A]age[B] > 100 && age[A] < 100
Otherwise, A will friend request B.
Note that if A requests B, B does not necessarily request A. Also, people will not friend request themselves.
How many total friend requests are made?
Example 1:
Input: [16,16] Output: 2 Explanation: 2 people friend request each other.
Example 2:
Input: [16,17,18] Output: 2 Explanation: Friend requests are made 17 -> 16, 18 -> 17.
Example 3:
Input: [20,30,100,110,120] Output: Explanation: Friend requests are made 110 -> 100, 120 -> 110, 120 -> 100.
Notes:
1 <= ages.length <= 20000.1 <= ages[i] <= 120.
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Intuition
Running a cross product of age array will be N 2 - quite slow
Instead we can process the count of ages of people since thats ~ 120, loop will be much faster
For every valid page pair
ans += ageA * ageB
if (ageA == ageB) => exclude self friend request => ans -= ageA
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Running a cross product of age array will be N 2 - quite slow
Instead we can process the count of ages of people since thats ~ 120, loop will be much faster
For every valid page pair
ans += ageA * ageB
if (ageA == ageB) => exclude self friend request => ans -= ageA
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