June 2018 Update

Task/Aliquot-sequence-classifications/Go/aliquot-sequence-classifications.go

@@ -0,0 +1,109 @@
+package main
+
+import (
+    "fmt"
+    "math"
+    "strings"
+)
+
+const threshold = uint64(1) << 47
+
+func indexOf(s []uint64, search uint64) int {
+    for i, e := range s {
+        if e == search {
+            return i
+        }
+    }
+    return -1
+}
+
+func contains(s []uint64, search uint64) bool {
+    return indexOf(s, search) > -1
+}
+
+func maxOf(i1, i2 int) int {
+    if i1 > i2 {
+        return i1
+    }
+    return i2
+}
+
+func sumProperDivisors(n uint64) uint64 {
+    if n < 2 {
+        return 0
+    }
+    sqrt := uint64(math.Sqrt(float64(n)))
+    sum := uint64(1)
+    for i := uint64(2); i <= sqrt; i++ {
+        if n % i != 0 {
+            continue
+        }
+        sum += i + n / i
+    }
+    if sqrt * sqrt == n {
+        sum -= sqrt
+    }
+    return sum
+}
+
+func classifySequence(k uint64) ([]uint64, string) {
+    if k == 0 {
+        panic("Argument must be positive.")
+    }
+    last := k
+    var seq []uint64
+    seq = append(seq, k)
+    for {
+        last = sumProperDivisors(last)
+        seq = append(seq, last)
+        n := len(seq)
+        aliquot := ""
+        switch {
+        case last == 0:
+            aliquot = "Terminating"
+        case n == 2 && last == k:
+            aliquot = "Perfect"
+        case n == 3 && last == k:
+            aliquot = "Amicable"
+        case n >= 4 && last == k:
+            aliquot = fmt.Sprintf("Sociable[%d]", n - 1)
+        case last == seq[n - 2]:
+            aliquot = "Aspiring"
+        case contains(seq[1 : maxOf(1, n - 2)], last):
+            aliquot = fmt.Sprintf("Cyclic[%d]", n - 1 - indexOf(seq[:], last))
+        case n == 16 || last > threshold:
+            aliquot = "Non-Terminating"
+        }
+        if aliquot != "" {
+            return seq, aliquot
+        }
+    }
+}
+
+func joinWithCommas(seq []uint64) string {
+    res := fmt.Sprint(seq)
+    res = strings.Replace(res, " ", ", ", -1)
+    return res
+}
+
+func main() {
+    fmt.Println("Aliquot classifications - periods for Sociable/Cyclic in square brackets:\n")
+    for k := uint64(1); k <= 10; k++ {
+        seq, aliquot := classifySequence(k)
+        fmt.Printf("%2d: %-15s %s\n", k, aliquot, joinWithCommas(seq))
+    }
+    fmt.Println()
+
+    s := []uint64{
+        11, 12, 28, 496, 220, 1184, 12496, 1264460, 790, 909, 562, 1064, 1488,
+    }
+    for _, k := range s {
+        seq, aliquot := classifySequence(k)
+        fmt.Printf("%7d: %-15s %s\n",  k, aliquot, joinWithCommas(seq))
+    }
+    fmt.Println()
+
+    k := uint64(15355717786080)
+    seq, aliquot := classifySequence(k)
+    fmt.Printf("%d: %-15s %s\n", k, aliquot, joinWithCommas(seq))
+}