825. Friends Of Appropriate Ages

最新推荐文章于 2021-06-14 21:20:44 发布

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最新推荐文章于 2021-06-14 21:20:44 发布

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分类专栏： LeetCode

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本文探讨了一种基于年龄限制的交友请求算法，通过设定特定条件来决定是否发送交友请求，包括年龄差、年龄上限等规则。举例说明了不同年龄组合下的交友请求情况，展示了算法的实现逻辑。

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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.

class Solution {
    public int numFriendRequests(int[] ages) {
        int len = ages.length;
        int cnt = 0;
        int[] counts = new int[121];
        for (int val : ages){
            counts[val] ++;
        }
        for (int i = 0; i < 121; ++ i){
            int countA = counts[i];
            for (int j = 0; j < 121; ++ j){
                if (!isValid(i, j)){
                    continue;
                }
                int countB = counts[j];
                cnt += countA*countB;
                if (i == j){
                    cnt -= countA;
                }
            }
        }
        return cnt;
    }
    
    public boolean isValid(int m, int n){
        double a = (double)m;
        double b = (double)n;
        if ((b <= 0.5*a + 7) || 
            (b > a) ||
            (b > 100 && a < 100)
           ){
            return false;
        }
        return true;
        
    }
}