AWK, C, Lua, Node.js and Perl solutions for week 119, part 2.

1 files changed, 39 insertions, 0 deletions

diff --git a/challenge-119/abigail/node/ch-2.js b/challenge-119/abigail/node/ch-2.js
new file mode 100644
index 0000000000..656c218f54
--- /dev/null
+++ b/challenge-119/abigail/node/ch-2.js
@@ -0,0 +1,39 @@
+#!/usr/local/bin/node
+
+//
+// See ../README.md
+//
+
+//
+// Run as: node ch-2.js < input-file
+//
+
+  require ('readline')
+. createInterface ({input: process . stdin})   
+. on              ('line', (num) => {
+    let number = "0";
+    for (let i = 0; i < + num; i ++) {
+        number = next_number (number)
+    }
+    console . log (number)
+})
+
+
+function next_number (prev_number) {
+    //
+    // Grab the trailing 3s (tail), its preceding number (num), and
+    // anything before that (prefix).
+    //
+    let [match, prefix, num, tail] =
+        ("0" + prev_number) . match (/^(.*)([012])(3*)$/)
+
+    //
+    // First, we take the prefix, and add (num + 1) to it,
+    // then the tail, where we have replaced each 3 by a 1.
+    // Then replace any '11' with '12' (we can only have 11s at the end).
+    // Finally, remove any leading 0.
+    //
+    return (prefix + (+ num + 1) + (tail . replace (/3/g,  "1"))) .
+                                           replace (/11/g, "12")  .
+                                           replace (/^0/,  "")
+}