2017 Day 23 Complete

2017/day23/day23-part2.go

@@ -0,0 +1,54 @@
+package main
+
+import (
+	"fmt"
+	"math"
+)
+
+func main() {
+	var a, b, c, d, e, f, g, h int
+	// Suppress go warnings
+	_, _, _, _, _, _, _, _ = a, b, c, d, e, f, g, h
+	// Derived from test.go
+	b = 109900
+	c = 126900
+
+	// Unoptimized:
+	/*
+		for ; b < c+1; b += 17 {
+			f = 1
+			for d = 2; d < b+1; d++ {
+				for e = 2; e < b+1; e++ {
+					if d*e == b {
+						f = 0
+					}
+				}
+			}
+			// When is f 0?
+			// when d*e == b for "certain values" of b
+			fmt.Println(d, e, b)
+			if f == 0 {
+				h++
+			}
+			// b = 109900
+		}
+	*/
+
+	// Optimized
+	for ; b < c+1; b += 17 {
+		if !IsPrime(b) {
+			h++
+		}
+	}
+
+	fmt.Println(h)
+}
+
+func IsPrime(value int) bool {
+	for i := 2; i <= int(math.Floor(float64(value)/2)); i++ {
+		if value%i == 0 {
+			return false
+		}
+	}
+	return value > 1
+}