add new solutions

solutions/13/q1390/solution.go

@@ -0,0 +1,45 @@
+package q1390
+
+import "slices"
+
+func sfd(n int) int {
+	if n < 6 {
+		return 0
+	}
+
+	buf := [6]int{1, n}
+	divisors := buf[:2]
+	nn := n
+	for i := 2; i*i <= nn; i++ {
+		for nn%i == 0 {
+			nn /= i
+
+			if !slices.Contains(divisors, i) {
+				divisors = append(divisors, i)
+			}
+			if !slices.Contains(divisors, nn) {
+				divisors = append(divisors, nn)
+			}
+			if !slices.Contains(divisors, n/nn) {
+				divisors = append(divisors, n/nn)
+			}
+			if len(divisors) > 4 {
+				return 0
+			}
+		}
+	}
+	if len(divisors) == 4 {
+		return divisors[0] + divisors[1] + divisors[2] + divisors[3]
+	}
+	return 0
+}
+
+func sumFourDivisors(nums []int) int {
+	sum := 0
+	for _, n := range nums {
+		sum += sfd(n)
+	}
+	return sum
+}
+
+var _ = sumFourDivisors