From 3513724df0310e8f414f7b145ec6be7d200bfd72 Mon Sep 17 00:00:00 2001
From: VicRen <vic.ren@me.com>
Date: Sun, 22 Nov 2020 23:09:18 +0800
Subject: [PATCH] 49: prime permutations

---
 49_prime_permutations/main.go      | 50 ++++++++++++++++++++++++++++++
 49_prime_permutations/main_test.go | 38 +++++++++++++++++++++++
 2 files changed, 88 insertions(+)
 create mode 100644 49_prime_permutations/main.go
 create mode 100644 49_prime_permutations/main_test.go

diff --git a/49_prime_permutations/main.go b/49_prime_permutations/main.go
new file mode 100644
index 0000000..3effc52
--- /dev/null
+++ b/49_prime_permutations/main.go
@@ -0,0 +1,50 @@
+package main
+
+import "fmt"
+
+func main() {
+	for a := 1489; a < 3340; a++ {
+		b := a + 3330
+		c := b + 3330
+		if isPrime(a) && isPrime(b) && isPrime(c) && isPerm(a, b) && isPerm(b, c) {
+			fmt.Println((a*10000+b)*10000 + c)
+		}
+	}
+}
+
+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
+}
+
+func isPerm(a, b int) bool {
+	cnt := []int{0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
+	for a > 0 {
+		cnt[a%10]++
+		a = a / 10
+	}
+	for b > 0 {
+		cnt[b%10]--
+		b = b / 10
+	}
+	for _, n := range cnt {
+		if n != 0 {
+			return false
+		}
+	}
+	return true
+}
diff --git a/49_prime_permutations/main_test.go b/49_prime_permutations/main_test.go
new file mode 100644
index 0000000..4d85553
--- /dev/null
+++ b/49_prime_permutations/main_test.go
@@ -0,0 +1,38 @@
+package main
+
+import "testing"
+
+func Test_isPerm(t *testing.T) {
+	type args struct {
+		a int
+		b int
+	}
+	tests := []struct {
+		name string
+		args args
+		want bool
+	}{
+		{
+			"test_1",
+			args{123, 321},
+			true,
+		},
+		{
+			"test_2",
+			args{123, 213},
+			true,
+		},
+		{
+			"test_3",
+			args{123, 211},
+			false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := isPerm(tt.args.a, tt.args.b); got != tt.want {
+				t.Errorf("isPerm() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}