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.
Notes:
- 1 <= ages.length <= 20000.
- 1 <= ages[i] <= 120.
Solution1:(TLE)
class Solution:
def numFriendRequests(self, ages):
"""
:type ages: List[int]
:rtype: int
"""
def friend(a,b):
return not (b<=0.5*a+7 or b>a or (b>100 and a<100))
res = 0
for i in range(len(ages)):
for j in range(i+1,len(ages)):
if friend(ages[i],ages[j]):
res += 1
if friend(ages[j],ages[i]):
res += 1
return res
73 / 83 test cases passed.
Solution2:(TLE)
class Solution:
def numFriendRequests(self, ages):
"""
:type ages: List[int]
:rtype: int
"""
def friend(a,b):
return not (b<=0.5*a+7)
ages.sort()
res = 0
dic = {}
for i in range(len(ages)):
if ages[i] not in dic:
temp = 0
for j in range(i+1,len(ages)):
if friend(ages[j],ages[i]):
temp += 1
dic[ages[i]] = temp
res += temp
else:
res += dic[ages[i]]
return res
78 / 83 test cases passed.
Solution3:
注意到age是有范围的
class Solution:
def numFriendRequests(self, ages):
"""
:type ages: List[int]
:rtype: int
"""
count = [0 for i in range(121)]
for i in ages:
count[i] += 1
res = 0
for i in range(1,121):
if count[i]==0:
continue
temp = i//2 + 8
res += count[i] * sum(count[temp:i])
if i>14:
res += count[i]*(count[i]-1)
return res