42: coded triangle numbers

42_coded_triangle_numbers/main.go

@@ -0,0 +1,63 @@
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"strings"
+)
+
+const BASE = 64
+
+func main() {
+	b, err := ioutil.ReadFile("p042_words.txt")
+	if err != nil {
+		panic(err)
+	}
+
+	word := readWords(string(b))
+	count := 0
+	for _, w := range word {
+		if isTriangleNumber(worthOf(w)) {
+			count++
+		}
+	}
+	fmt.Println("count:", count)
+}
+
+func readWords(s string) []string {
+	if len(s) == 0 {
+		return nil
+	}
+	str := strings.Replace(s, "\"", "", -1)
+	ret := strings.Split(str, ",")
+	return ret
+}
+
+func worthOf(word string) int {
+	if len(word) == 0 {
+		return 0
+	}
+	sum := 0
+	for i := 0; i < len(word); i++ {
+		a := word[i : i+1][0]
+		w := uint8(a) - BASE
+		sum += int(w)
+	}
+	return sum
+}
+
+func isTriangleNumber(n int) bool {
+	//tn = ½n(n+1)
+	x := 2 * n
+	res := x
+	//牛顿法求平方根
+	for res*res > x {
+		res = (res + x/res) / 2
+	}
+	for i := res; i > 0; i-- {
+		if i*(i+1) == x {
+			return true
+		}
+	}
+	return false
+}