leetcode 825. Friends Of Appropriate Ages

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原題地址：https://leetcode.com/problems/friends-of-appropriate-ages/

題目

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] + 7*

• age[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.

Note:

• 1 <= ages.length <= 20000.
• 1 <= ages[i] <= 120.

python代碼

class Solution:def numFriendRequests(self, ages):""":type ages: List[int]:rtype: int"""age = collections.Counter(ages)res=0for A in age:for B in age:if A == B:if B<=0.5*A+7 or B>A or (B>100 and A<100): continueres += (age[A] * (age[A]-1))else:if B<=0.5*A+7 or B>A or (B>100 and A<100): continueres += age[A] * age[B]return res

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