825_Friends_Of_Appropriate_Ages

Author: Partho Biswas

README.md

@@ -189,6 +189,7 @@ I have solved quite a number of problems from several topics. See the below tabl
 |75| **[311. Sparse Matrix Multiplication](https://tinyurl.com/y9lapcjx)** | [Python](https://tinyurl.com/wu6rdaw/311_Sparse_Matrix_Multiplication.py), [Swift](https://tinyurl.com/wuja3c4/311_Sparse_Matrix_Multiplication.swift) | [Art 1](https://tinyurl.com/ycv24vc4), [Art 2](https://tinyurl.com/ycmqcfw9), [Art 3](https://tinyurl.com/y9az7nef), **[Art 4](https://tinyurl.com/y84lwkya)** | Medium | Very tricky  |
 |76| **[896. Monotonic Array](https://tinyurl.com/y8a95fb6)** | [Python](https://tinyurl.com/wu6rdaw/896_Monotonic_Array.py), [Swift](https://tinyurl.com/wuja3c4/896_Monotonic_Array.swift) | --- | Eassy |  |
 |77| **[670. Maximum Swap](https://tinyurl.com/y2zhdd33)** | [Python](https://tinyurl.com/wu6rdaw/670_Maximum_Swap.py), [Swift](https://tinyurl.com/wuja3c4/670_Maximum_Swap.swift) | [Art 1](https://tinyurl.com/y8vqklj3) | Medium |  |
+|78| **[825. Friends Of Appropriate Ages](https://tinyurl.com/ycgnqxb8)** | [Python](https://tinyurl.com/wu6rdaw/825_Friends_Of_Appropriate_Ages.py), [Swift](https://tinyurl.com/wuja3c4/825_Friends_Of_Appropriate_Ages.swift) | [Art 1](https://tinyurl.com/yd4oal3l) | Medium | Think differently from a different angle. Loved this problem |
 
 
 </p>

leetcode.com/swift/DS_ALGO_PRAC.playground/Contents.swift

@@ -1,2 +1 @@
-import Foundation
 

leetcode.com/swift/DS_ALGO_PRAC.playground/Sources/swift/825_Friends_Of_Appropriate_Ages.swift

@@ -0,0 +1,64 @@
+
+// Brute force approach. Time: O(n^2)
+// Time Limit Exceeded
+import Foundation
+class Solution {
+    func numFriendRequests(_ ages: [Int]) -> Int {
+        let contertedAges = ages.map {Double($0)}
+        var existingRequestSet = Set<String>()
+        for A in 0..<contertedAges.count {
+            for B in 0..<contertedAges.count {
+                if A == B {
+                    continue
+                }
+                if contertedAges[B] <= (0.5 * contertedAges[A] + 7) {
+                    continue
+                }
+                if contertedAges[B] > contertedAges[A] {
+                    continue
+                }
+                if contertedAges[B] > 100 && contertedAges[A] < 100 {
+                    continue
+                }
+                let requestKey = "\(A)-\(B)"
+                if !existingRequestSet.contains(requestKey) {
+                    existingRequestSet.insert(requestKey)
+                }
+            }
+        }
+        return existingRequestSet.count
+    }
+}
+
+
+// Brute force approach. Time: O(1)
+import Foundation
+class Solution {
+    func numFriendRequests(_ ages: [Int]) -> Int {
+        let convertedAges = ages.map {Double($0)}
+        var ageCount = [Double: Int]()
+        for (index, item) in convertedAges.enumerated() {
+            ageCount[item, default: 0] += 1
+        }
+        
+        var requestSent = 0
+        for (ageA, countA) in ageCount {
+            for (ageB, countB) in ageCount {
+                if ageB <= (0.5 * ageA + 7) {
+                    continue
+                }
+                if ageB > ageA {
+                    continue
+                }
+                if ageB > 100 && ageA < 100 {
+                    continue
+                }
+                if ageA == ageB {
+                    requestSent -= countA
+                }
+                requestSent += (countA * countB)
+            }
+        }
+        return requestSent
+    }
+}