tasks a-s

Task/Self-referential-sequence/D/self-referential-sequence-1.d

@@ -0,0 +1,37 @@
+import std.stdio, std.algorithm, std.conv;
+
+string[] selfReferentialSeq(string n, string[] seen=[]) {
+    static string[][string] cache;
+    if (n in cache) return cache[n];
+    if (canFind(seen, n)) return [];
+
+    int[10] digit_count;
+    foreach (d; n)
+        digit_count[d - '0']++;
+    string term;
+    foreach_reverse (d; 0 .. 10)
+        if (digit_count[d] > 0)
+            term ~= text(digit_count[d], d);
+    return cache[n] = [n] ~ selfReferentialSeq(term, [n] ~ seen);
+}
+
+void main() {
+    enum int limit = 1_000_000;
+    int max_len;
+    int[] max_vals;
+
+    foreach (n; 1 .. limit) {
+        const seq = n.text().selfReferentialSeq();
+        if (seq.length > max_len) {
+            max_len = seq.length;
+            max_vals = [n];
+        } else if (seq.length == max_len)
+            max_vals ~= n;
+    }
+
+    writeln("values: ", max_vals);
+    writeln("iterations: ", max_len);
+    writeln("sequence:");
+    foreach (idx, val; max_vals[0].text().selfReferentialSeq())
+        writefln("%2d %s", idx + 1, val);
+}