49: prime permutations

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
+}