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]
+}

26_reciprocal_cycles/main_test.go

@@ -0,0 +1,55 @@
+package main
+
+import (
+	"reflect"
+	"testing"
+)
+
+func Test_findDecimalOfOneNth(t *testing.T) {
+	type args struct {
+		n int
+	}
+	tt := []struct {
+		name string
+		args args
+		want int
+	}{
+		{
+			"2",
+			args{2},
+			1,
+		},
+		{
+			"4",
+			args{4},
+			2,
+		},
+		{
+			"6",
+			args{6},
+			1,
+		},
+		{
+			"7",
+			args{7},
+			6,
+		},
+		{
+			"10",
+			args{10},
+			1,
+		},
+		{
+			"100",
+			args{100},
+			2,
+		},
+	}
+	for _, tc := range tt {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := findCycleLengthOfOneNth(tc.args.n); !reflect.DeepEqual(got, tc.want) {
+				t.Errorf("findCycleLengthOfOneNth() = %v, want %v", got, tc.want)
+			}
+		})
+	}
+}