tasks a-s

Task/Roman-numerals-Decode/D/roman-numerals-decode-1.d

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+import std.regex, std.algorithm;
+
+int toArabic(in string s) /*pure nothrow*/ {
+    static immutable weights = [1000, 900, 500, 400, 100,
+                                90, 50, 40, 10, 9, 5, 4, 1];
+    static immutable symbols = ["M","CM","D","CD","C","XC",
+                                "L","XL","X","IX","V","IV","I"];
+
+    int arabic;
+    foreach (m; s.match(regex(r"CM|CD|XC|XL|IX|IV|[MDCLXVI]", "g")))
+        arabic += weights[symbols.countUntil(m.hit)];
+    return arabic;
+}
+
+void main() {
+    assert(toArabic("MCMXC") == 1990);
+    assert(toArabic("MMVIII") == 2008);
+    assert(toArabic("MDCLXVI") == 1666);
+}

Task/Roman-numerals-Decode/D/roman-numerals-decode-2.d

@@ -0,0 +1,20 @@
+import std.regex, std.algorithm;
+
+immutable int[string] w2s;
+
+nothrow static this() {
+    w2s = ["IX":  9, "C":  100, "D":  500, "CM": 900, "I":   1,
+           "XC": 90, "M": 1000, "L":   50, "CD": 400, "XL": 40,
+           "V":   5, "X":   10, "IV":   4];
+}
+
+int toArabic(in string s) /*pure nothrow*/ {
+    auto ms = match(s, regex("CM|CD|XC|XL|IX|IV|[MDCLXVI]", "g"));
+    return reduce!((a, m) => a + w2s[m.hit])(0, ms);
+}
+
+void main() {
+    assert("MCMXC".toArabic == 1990);
+    assert("MMVIII".toArabic == 2008);
+    assert("MDCLXVI".toArabic == 1666);
+}