From 681c9a12b871fbe18d33004aea527e0f089dc59e Mon Sep 17 00:00:00 2001
From: VicRen <vic.ren@me.com>
Date: Thu, 19 Nov 2020 11:36:28 +0800
Subject: [PATCH] 47: distinct primes factors

---
 47_distinct_primes_factors/main.go      | 71 +++++++++++++++++++++++++
 47_distinct_primes_factors/main_test.go | 40 ++++++++++++++
 2 files changed, 111 insertions(+)
 create mode 100644 47_distinct_primes_factors/main.go
 create mode 100644 47_distinct_primes_factors/main_test.go

diff --git a/47_distinct_primes_factors/main.go b/47_distinct_primes_factors/main.go
new file mode 100644
index 0000000..80a01c7
--- /dev/null
+++ b/47_distinct_primes_factors/main.go
@@ -0,0 +1,71 @@
+package main
+
+import (
+	"fmt"
+	"math"
+	"sort"
+)
+
+func main() {
+	nums := make([]int, 0)
+	i := 2
+	for {
+		primes := distinctPrimesOf(i)
+		if len(primes) == 4 {
+			l := len(nums)
+			if l == 0 || (nums[l-1] == i-1) {
+				nums = append(nums, i)
+			} else {
+				nums = []int{i}
+			}
+			if len(nums) == 4 {
+				break
+			}
+		}
+		i++
+	}
+	fmt.Println(nums)
+}
+
+func distinctPrimesOf(n int) []int {
+	m := make(map[int]struct{})
+	max := int(math.Sqrt(float64(n)))
+	divider := 2
+	for divider <= max {
+		if n%divider == 0 {
+			if isPrime(divider) {
+				m[divider] = struct{}{}
+			}
+			x := n / divider
+			if isPrime(x) {
+				m[x] = struct{}{}
+			}
+		}
+		divider++
+	}
+	var ret []int
+	for k := range m {
+		ret = append(ret, k)
+	}
+	sort.Ints(ret)
+	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/47_distinct_primes_factors/main_test.go b/47_distinct_primes_factors/main_test.go
new file mode 100644
index 0000000..aaed401
--- /dev/null
+++ b/47_distinct_primes_factors/main_test.go
@@ -0,0 +1,40 @@
+package main
+
+import (
+	"reflect"
+	"testing"
+)
+
+func Test_distinctPrimesOf(t *testing.T) {
+	type args struct {
+		n int
+	}
+	tests := []struct {
+		name string
+		args args
+		want []int
+	}{
+		{
+			"4",
+			args{4},
+			[]int{2},
+		},
+		{
+			"14",
+			args{14},
+			[]int{2, 7},
+		},
+		{
+			"644",
+			args{644},
+			[]int{2, 7, 23},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := distinctPrimesOf(tt.args.n); !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("distinctPrimesOf() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}