June 2018 Update

Task/Number-names/Go/number-names.go

@@ -3,52 +3,56 @@ package main
 import "fmt"
 
 func main() {
-    for _, n := range []int64{12, 1048576, 9e18} {
-        fmt.Println(say(n))
-    }
+	for _, n := range []int64{12, 1048576, 9e18, -2, 0} {
+		fmt.Println(say(n))
+	}
 }
 
-var small = []string{"", "one", "two", "three", "four", "five", "six",
-    "seven", "eight", "nine", "ten", "eleven", "twelve", "thirteen",
-    "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen"}
-var tens = []string{"ones", "ten", "twenty", "thirty", "forty",
-    "fifty", "sixty", "seventy", "eighty", "ninety"}
-var illions = []string{"thousand", "million", "billion",
-    "trillion", "quadrillion", "quintillion"}
+var small = [...]string{"zero", "one", "two", "three", "four", "five", "six",
+	"seven", "eight", "nine", "ten", "eleven", "twelve", "thirteen",
+	"fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen"}
+var tens = [...]string{"", "", "twenty", "thirty", "forty",
+	"fifty", "sixty", "seventy", "eighty", "ninety"}
+var illions = [...]string{"", " thousand", " million", " billion",
+	" trillion", " quadrillion", " quintillion"}
 
 func say(n int64) string {
-    switch {
-    case n < 1:
-    case n < 20:
-        return small[n]
-    case n < 100:
-        t := tens[n/10]
-        s := n % 10
-        if s > 0 {
-            t += " " + small[s]
-        }
-        return t
-    case n < 1000:
-        h := small[n/100] + " hundred"
-        s := n % 100
-        if s > 0 {
-            h += " " + say(s)
-        }
-        return h
-    default:
-        sx := say(n % 1000)
-        for i := 0; n >= 1000; i++ {
-            n /= 1000
-            p := n % 1000
-            if p > 0 {
-                ix := say(p) + " " + illions[i]
-                if sx > "" {
-                    ix += " " + sx
-                }
-                sx = ix
-            }
-        }
-        return sx
-    }
-    return ""
+	var t string
+	if n < 0 {
+		t = "negative "
+		// Note, for math.MinInt64 this leaves n negative.
+		n = -n
+	}
+	switch {
+	case n < 20:
+		t += small[n]
+	case n < 100:
+		t += tens[n/10]
+		s := n % 10
+		if s > 0 {
+			t += "-" + small[s]
+		}
+	case n < 1000:
+		t += small[n/100] + " hundred"
+		s := n % 100
+		if s > 0 {
+			t += " " + say(s)
+		}
+	default:
+		// work right-to-left
+		sx := ""
+		for i := 0; n > 0; i++ {
+			p := n % 1000
+			n /= 1000
+			if p > 0 {
+				ix := say(p) + illions[i]
+				if sx != "" {
+					ix += " " + sx
+				}
+				sx = ix
+			}
+		}
+		t += sx
+	}
+	return t
 }