26: reciprocal cycles

26_reciprocal_cycles/main.go

@@ -0,0 +1,34 @@
+package main
+
+import "fmt"
+
+func main() {
+	max := 0
+	d := 1
+	for d < 1000 {
+		n := findCycleLengthOfOneNth(d)
+		if n > max {
+			max = d
+		}
+		d++
+	}
+	fmt.Println("max:", max)
+}
+
+func findCycleLengthOfOneNth(n int) int {
+	m := map[int]int{}
+	a := 1
+	t := 0
+	for {
+		if _, ok := m[a]; ok {
+			break
+		}
+		m[a] = t
+		a = a % n * 10
+		if a == 0 {
+			return t
+		}
+		t++
+	}
+	return t - m[a]
+}