Data commit

Task/Zumkeller-numbers/Go/zumkeller-numbers.go

@@ -0,0 +1,91 @@
+package main
+
+import "fmt"
+
+func getDivisors(n int) []int {
+    divs := []int{1, n}
+    for i := 2; i*i <= n; i++ {
+        if n%i == 0 {
+            j := n / i
+            divs = append(divs, i)
+            if i != j {
+                divs = append(divs, j)
+            }
+        }
+    }
+    return divs
+}
+
+func sum(divs []int) int {
+    sum := 0
+    for _, div := range divs {
+        sum += div
+    }
+    return sum
+}
+
+func isPartSum(divs []int, sum int) bool {
+    if sum == 0 {
+        return true
+    }
+    le := len(divs)
+    if le == 0 {
+        return false
+    }
+    last := divs[le-1]
+    divs = divs[0 : le-1]
+    if last > sum {
+        return isPartSum(divs, sum)
+    }
+    return isPartSum(divs, sum) || isPartSum(divs, sum-last)
+}
+
+func isZumkeller(n int) bool {
+    divs := getDivisors(n)
+    sum := sum(divs)
+    // if sum is odd can't be split into two partitions with equal sums
+    if sum%2 == 1 {
+        return false
+    }
+    // if n is odd use 'abundant odd number' optimization
+    if n%2 == 1 {
+        abundance := sum - 2*n
+        return abundance > 0 && abundance%2 == 0
+    }
+    // if n and sum are both even check if there's a partition which totals sum / 2
+    return isPartSum(divs, sum/2)
+}
+
+func main() {
+    fmt.Println("The first 220 Zumkeller numbers are:")
+    for i, count := 2, 0; count < 220; i++ {
+        if isZumkeller(i) {
+            fmt.Printf("%3d ", i)
+            count++
+            if count%20 == 0 {
+                fmt.Println()
+            }
+        }
+    }
+    fmt.Println("\nThe first 40 odd Zumkeller numbers are:")
+    for i, count := 3, 0; count < 40; i += 2 {
+        if isZumkeller(i) {
+            fmt.Printf("%5d ", i)
+            count++
+            if count%10 == 0 {
+                fmt.Println()
+            }
+        }
+    }
+    fmt.Println("\nThe first 40 odd Zumkeller numbers which don't end in 5 are:")
+    for i, count := 3, 0; count < 40; i += 2 {
+        if (i % 10 != 5) && isZumkeller(i) {
+            fmt.Printf("%7d ", i)
+            count++
+            if count%8 == 0 {
+                fmt.Println()
+            }
+        }
+    }
+    fmt.Println()
+}