Data commit

Task/Roman-numerals-Decode/Go/roman-numerals-decode-1.go

@@ -0,0 +1,84 @@
+package main
+
+import (
+    "errors"
+    "fmt"
+)
+
+var m = map[rune]int{
+    'I': 1,
+    'V': 5,
+    'X': 10,
+    'L': 50,
+    'C': 100,
+    'D': 500,
+    'M': 1000,
+}
+
+func parseRoman(s string) (r int, err error) {
+    if s == "" {
+        return 0, errors.New("Empty string")
+    }
+    is := []rune(s) // easier to convert string up front
+    var c0 rune     // c0: roman character last read
+    var cv0 int     // cv0: value of cv
+
+    // the key to the algorithm is to process digits from right to left
+    for i := len(is) - 1; i >= 0; i-- {
+        // read roman digit
+        c := is[i]
+        k := c == '\u0305' // unicode overbar combining character
+        if k {
+            if i == 0 {
+                return 0, errors.New(
+                    "Overbar combining character invalid at position 0")
+            }
+            i--
+            c = is[i]
+        }
+        cv := m[c]
+        if cv == 0 {
+            if c == 0x0305 {
+                return 0, fmt.Errorf(
+                    "Overbar combining character invalid at position %d", i)
+            } else {
+                return 0, fmt.Errorf(
+                    "Character unrecognized as Roman digit: %c", c)
+            }
+        }
+        if k {
+            c = -c // convention indicating overbar
+            cv *= 1000
+        }
+
+        // handle cases of new, same, subtractive, changed, in that order.
+        switch {
+        default: // case 4: digit change
+            fallthrough
+        case c0 == 0: // case 1: no previous digit
+            c0 = c
+            cv0 = cv
+        case c == c0: // case 2: same digit
+        case cv*5 == cv0 || cv*10 == cv0: // case 3: subtractive
+            // handle next digit as new.
+            // a subtractive digit doesn't count as a previous digit.
+            c0 = 0
+            r -= cv  // subtract...
+            continue // ...instead of adding
+        }
+        r += cv // add, in all cases except subtractive
+    }
+    return r, nil
+}
+
+func main() {
+    // parse three numbers mentioned in task description
+    for _, r := range []string{"MCMXC", "MMVIII", "MDCLXVI"} {
+        v, err := parseRoman(r)
+        if err != nil {
+            fmt.Println(err)
+        } else {
+            fmt.Println(r, "==", v)
+        }
+    }
+}

Task/Roman-numerals-Decode/Go/roman-numerals-decode-2.go

@@ -0,0 +1,37 @@
+package main
+
+import (
+	"fmt"
+)
+
+var m = map[rune]int{
+	'I': 1,
+	'V': 5,
+	'X': 10,
+	'L': 50,
+	'C': 100,
+	'D': 500,
+	'M': 1000,
+}
+
+// function, per task description
+func from_roman(roman string) (arabic int) {
+	last_digit := 1000
+	for _, r := range roman {
+		digit := m[r]
+		if last_digit < digit {
+			arabic -= 2 * last_digit
+		}
+		last_digit = digit
+		arabic += digit
+	}
+
+	return arabic
+}
+
+func main() {
+	// parse three numbers mentioned in task description
+	for _, roman_digit := range []string{"MCMXC", "MMVIII", "MDCLXVI"} {
+		fmt.Printf("%-10s == %d\n", roman_digit, from_roman(roman_digit))
+	}
+}