LeetCode 825 适龄的朋友

LeetCode 825 适龄的朋友

看完条件一晃眼...好像叫德摩根定律? (似乎是离散数学里的)

反正展开就对了

为了表达方便修改了运算符

  !( b<=0.5*a+7 || b>a || (b>100 && a<100)) 
= !(b<=0.5*a+7) && !(b>a) || !(b>100 && a<100)
= b>0.5*a+7 && b<=a && (b<=100 || a>=100)
= b>0.5*a+7 && b<=a

故

b ∈ (14, +∞)
a ∈ [b, 2b-14)

此时直接套二分搜索就差不多了。至于还能用计数优化什么的就不搞了(懒

Python3

from typing import List
import bisect

class Solution:
    def numFriendRequests(self, ages: List[int]) -> int:
        ages = sorted([x for x in filter(lambda x: x>14, ages)])

        opt = 0
        lastV, lastS = -1, -1
        for i, v in enumerate(ages):
            if v == lastV:
                opt += lastS
                continue
            if i+1 == len(ages):
                continue

            lastV, lastS = v, 0
            ed = bisect.bisect_left(ages, 2*v - 14, i)
            if ed:
                lastS = ed - i - 1
                opt += lastS
        return opt