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825. Friends Of Appropriate Ages
Description
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:
age[y] <= 0.5 * age[x] + 7
age[y] > age[x]
age[y] > 100 && age[x] < 100
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.
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 * 104
1 <= ages[i] <= 120
Solutions
-
class Solution { public int numFriendRequests(int[] ages) { int[] counter = new int[121]; for (int age : ages) { ++counter[age]; } int ans = 0; for (int i = 1; i < 121; ++i) { int n1 = counter[i]; for (int j = 1; j < 121; ++j) { int n2 = counter[j]; if (!(j <= 0.5 * i + 7 || j > i || (j > 100 && i < 100))) { ans += n1 * n2; if (i == j) { ans -= n2; } } } } return ans; } }
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class Solution { public: int numFriendRequests(vector<int>& ages) { vector<int> counter(121); for (int age : ages) ++counter[age]; int ans = 0; for (int i = 1; i < 121; ++i) { int n1 = counter[i]; for (int j = 1; j < 121; ++j) { int n2 = counter[j]; if (!(j <= 0.5 * i + 7 || j > i || (j > 100 && i < 100))) { ans += n1 * n2; if (i == j) ans -= n2; } } } return ans; } };
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class Solution: def numFriendRequests(self, ages: List[int]) -> int: counter = Counter(ages) ans = 0 for i in range(1, 121): n1 = counter[i] for j in range(1, 121): n2 = counter[j] if not (j <= 0.5 * i + 7 or j > i or (j > 100 and i < 100)): ans += n1 * n2 if i == j: ans -= n2 return ans
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func numFriendRequests(ages []int) int { counter := make([]int, 121) for _, age := range ages { counter[age]++ } ans := 0 for i := 1; i < 121; i++ { n1 := counter[i] for j := 1; j < 121; j++ { n2 := counter[j] if !(j <= i/2+7 || j > i || (j > 100 && i < 100)) { ans += n1 * n2 if i == j { ans -= n2 } } } } return ans }