Data commit

Task/Amicable-pairs/Swift/amicable-pairs-1.swift

@@ -0,0 +1,54 @@
+import func Darwin.sqrt
+
+func sqrt(x:Int) -> Int { return Int(sqrt(Double(x))) }
+
+func properDivs(n: Int) -> [Int] {
+
+    if n == 1 { return [] }
+
+    var result = [Int]()
+
+    for div in filter (1...sqrt(n), { n % $0 == 0 }) {
+
+        result.append(div)
+
+        if n/div != div && n/div != n { result.append(n/div) }
+    }
+
+    return sorted(result)
+
+}
+
+
+func sumDivs(n:Int) -> Int {
+
+    struct Cache { static var sum = [Int:Int]() }
+
+    if let sum = Cache.sum[n] { return sum }
+
+    let sum = properDivs(n).reduce(0) { $0 + $1 }
+
+    Cache.sum[n] = sum
+
+    return sum
+}
+
+func amicable(n:Int, m:Int) -> Bool {
+
+    if n == m { return false }
+
+    if sumDivs(n) != m || sumDivs(m) != n { return false }
+
+    return true
+}
+
+var pairs = [(Int, Int)]()
+
+for n in 1 ..< 20_000 {
+    for m in n+1 ... 20_000 {
+        if amicable(n, m) {
+            pairs.append(n, m)
+            println("\(n, m)")
+        }
+    }
+}

Task/Amicable-pairs/Swift/amicable-pairs-2.swift

@@ -0,0 +1,44 @@
+import func Darwin.sqrt
+
+func sqrt(x:Int) -> Int { return Int(sqrt(Double(x))) }
+
+func sigma(n: Int) -> Int {
+
+    if n == 1 { return 0 }          // definition of aliquot sum
+
+    var result = 1
+    let root = sqrt(n)
+
+    for var div = 2; div <= root; ++div {
+        if n % div == 0 {
+            result += div + n/div
+        }
+
+    }
+    if root*root == n { result -= root }
+
+    return (result)
+}
+
+func amicables (upTo: Int) -> () {
+
+    var aliquot = Array(count: upTo+1, repeatedValue: 0)
+
+    for i in 1 ... upTo {           // fill lookup array
+        aliquot[i] = sigma(i)
+    }
+
+ for i in 1 ... upTo {
+        let a = aliquot[i]
+        if a > upTo {continue}      //second part of pair out-of-bounds
+
+        if a == i {continue}        //skip perfect numbers
+
+        if i == aliquot[a] {
+            print("\(i, a)")
+            aliquot[a] = upTo+1     //prevent second display of pair
+        }
+    }
+}
+
+amicables(20_000)