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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.

---

人們會互相發送好友請求，現在給定一個包含有他們年齡的數組，ages[i]?表示第 i 個人的年齡。

當滿足以下條件時，A 不能給 B（A、B不為同一人）發送好友請求：

• age[B]?<= 0.5 * age[A]?+ 7
• age[B]?> age[A]
• age[B]?> 100 &&?age[A]?< 100

否則，A 可以給 B 發送好友請求。

注意如果 A 向 B 發出了請求，不等于 B 接受了 A 的請求。而且，人們不會給自己發送好友請求。?

求總共會發出多少份好友請求?

示例 1:

輸入: [16,16] 輸出: 2 解釋: 二人可以互發好友申請。

示例 2:

輸入: [16,17,18] 輸出: 2 解釋: 好友請求可產生于 17 -> 16, 18 -> 17.

示例 3:

輸入: [20,30,100,110,120] 輸出: 3 解釋: 好友請求可產生于 110 -> 100, 120 -> 110, 120 -> 100.

說明:

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

---

Runtime:?240 ms Memory Usage:?19.4 MB 1 class Solution { 2 func numFriendRequests(_ ages: [Int]) -> Int { 3 var res:Int = 0 4 var numInAge:[Int] = [Int](repeating:0,count:121) 5 var sumInAge:[Int] = [Int](repeating:0,count:121) 6 for age in ages 7 { 8 numInAge[age] += 1 9 } 10 for i in 1...120 11 { 12 sumInAge[i] = numInAge[i] + sumInAge[i - 1] 13 } 14 for i in 15...120 15 { 16 if numInAge[i] == 0 {continue} 17 var cnt:Int = sumInAge[i] - sumInAge[Int(Double(i) * 0.5 + 7)] 18 res += cnt * numInAge[i] - numInAge[i] 19 } 20 return res 21 } 22 }

---

268ms

1 class Solution { 2 func numFriendRequests(_ ages: [Int]) -> Int { 3 var count = [Int](repeating: 0, count: 121) 4 for age in ages { count[age] += 1 } 5 6 var ans = 0 7 for ageA in 0...120 { 8 let countA = count[ageA] 9 for ageB in 0...120 { 10 let countB = count[ageB] 11 if (ageA + 14) >= 2*ageB { continue } 12 if ageA < ageB { continue } 13 if ageA < 100 && 100 < ageB { continue } 14 ans += countA * countB 15 if ageA == ageB { ans -= countA} 16 } 17 } 18 return ans 19 } 20 }

---

292ms

1 class Solution { 2 func numFriendRequests(_ ages: [Int]) -> Int { 3 var map = [Int: Int]() 4 for age in ages { 5 map[age] = (map[age] ?? 0) + 1 6 } 7 var result = 0 8 for i in 0...120 { 9 if let iCount = map[i] { 10 for j in 0...120 { 11 if let jCount = map[j] { 12 if j <= i / 2 + 7 || j > i || (j > 100 && i < 100) { 13 continue 14 } 15 if i == j { 16 result += (iCount - 1) * iCount 17 } else { 18 result += iCount * jCount 19 } 20 } 21 } 22 } 23 } 24 return result 25 } 26 }

---

404ms

1 class Solution { 2 func numFriendRequests(_ ages: [Int]) -> Int { 3 var ageCounts = [Int](repeating: 0, count: 121) 4 for age in ages { 5 ageCounts[age] += 1 6 } 7 var res = 0 8 for i in 0..<ageCounts.count { 9 var ageA = i 10 for j in 0..<ageCounts.count { 11 var ageB = j 12 if ageB <= Int(floor(0.5 * Double(ageA) + 7)) { continue } 13 if ageB > ageA { continue } 14 res += ageCounts[i] * ageCounts[j] 15 if ageA == ageB { 16 res -= ageCounts[i] 17 } 18 } 19 } 20 return res 21 } 22 }

?

轉載于:https://www.cnblogs.com/strengthen/p/10569342.html

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