From 3861deeed3c5439ff65b71c428e4893078be1695 Mon Sep 17 00:00:00 2001
From: VicRen <vic.ren@me.com>
Date: Thu, 5 Nov 2020 09:43:53 +0800
Subject: [PATCH] 35: circular primes

---
 35_circular_primes/main.go      |  70 +++++++++++++++++++++
 35_circular_primes/main_test.go | 104 ++++++++++++++++++++++++++++++++
 2 files changed, 174 insertions(+)
 create mode 100644 35_circular_primes/main.go
 create mode 100644 35_circular_primes/main_test.go

diff --git a/35_circular_primes/main.go b/35_circular_primes/main.go
new file mode 100644
index 0000000..2a260ff
--- /dev/null
+++ b/35_circular_primes/main.go
@@ -0,0 +1,70 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+)
+
+func main() {
+	saved := map[int]struct{}{}
+	for i := 2; i < 1e6; i++ {
+		fmt.Println("i:", i)
+		if _, ok := saved[i]; ok {
+			continue
+		}
+		ns := circularNumbersOf(i)
+		tmpMap := map[int]struct{}{}
+		for _, n := range ns {
+			if isPrime(n) {
+				tmpMap[n] = struct{}{}
+			}
+		}
+		if len(tmpMap) == len(ns) {
+			for k := range tmpMap {
+				saved[k] = struct{}{}
+			}
+		}
+	}
+	fmt.Println("num:", len(saved), saved)
+}
+
+func circularNumbersOf(n int) []int {
+	var ret []int
+	retMap := map[int]struct{}{}
+	ns := strconv.Itoa(n)
+	ret = append(ret, n)
+	retMap[n] = struct{}{}
+	l := len(ns)
+	if l < 2 {
+		return ret
+	}
+	for i := 1; i < l; i++ {
+		ns = ns[1:] + ns[:1]
+		num, _ := strconv.Atoi(ns)
+		if _, ok := retMap[num]; ok {
+			continue
+		}
+		retMap[num] = struct{}{}
+		ret = append(ret, num)
+	}
+	return ret
+}
+
+func isPrime(n int) bool {
+	if n <= 1 {
+		return false
+	}
+	res := n
+	//牛顿法求平方根
+	for res*res > n {
+		res = (res + n/res) / 2
+	}
+	divider := 2
+	for divider <= res {
+		if n%divider == 0 {
+			return false
+		}
+		divider++
+	}
+	return true
+}
diff --git a/35_circular_primes/main_test.go b/35_circular_primes/main_test.go
new file mode 100644
index 0000000..9e864aa
--- /dev/null
+++ b/35_circular_primes/main_test.go
@@ -0,0 +1,104 @@
+package main
+
+import (
+	"reflect"
+	"testing"
+)
+
+func Test_isPrime(t *testing.T) {
+	type args struct {
+		n int
+	}
+	tt := []struct {
+		name string
+		args args
+		want bool
+	}{
+		{
+			"1",
+			args{1},
+			false,
+		},
+		{
+			"2",
+			args{2},
+			true,
+		},
+		{
+			"4",
+			args{4},
+			false,
+		},
+		{
+			"17",
+			args{17},
+			true,
+		},
+		{
+			"37",
+			args{37},
+			true,
+		},
+		{
+			"73",
+			args{73},
+			true,
+		},
+		{
+			"13 * 3 * 5 * 5 * 17 * 31 * 737",
+			args{3 * 3 * 5 * 5 * 17 * 31 * 73},
+			false,
+		},
+		{
+			"large_one",
+			args{2876*2876 - 63*2876 + 977},
+			false,
+		},
+	}
+	for _, tc := range tt {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := isPrime(tc.args.n); got != tc.want {
+				t.Errorf("isPrime() = %v, want %v", got, tc.want)
+			}
+		})
+	}
+}
+
+func Test_circularNumbersOf(t *testing.T) {
+	type args struct {
+		n int
+	}
+	tests := []struct {
+		name string
+		args args
+		want []int
+	}{
+		{
+			"197",
+			args{197},
+			[]int{197, 971, 719},
+		},
+		{
+			"19",
+			args{19},
+			[]int{19, 91},
+		},
+		{
+			"11",
+			args{11},
+			[]int{11},
+		},
+		{
+			"12345",
+			args{12345},
+			[]int{12345, 23451, 34512, 45123, 51234},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := circularNumbersOf(tt.args.n); !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("circularNumbersOf() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}