2016 Update

Task/Self-referential-sequence/Lua/self-referential-sequence.lua

@@ -0,0 +1,53 @@
+-- Return the next term in the self-referential sequence
+function findNext (nStr)
+    local nTab, outStr, pos, count = {}, "", 1, 1
+    for i = 1, #nStr do nTab[i] = nStr:sub(i, i) end
+    table.sort(nTab, function (a, b) return a > b end)
+    while pos <= #nTab do
+        if nTab[pos] == nTab[pos + 1] then
+            count = count + 1
+        else
+            outStr = outStr .. count .. nTab[pos]
+            count = 1
+        end
+        pos = pos + 1
+    end
+    return outStr
+end
+
+-- Return boolean indicating whether table t contains string s
+function contains (t, s)
+    for k, v in pairs(t) do
+        if v == s then return true end
+    end
+    return false
+end
+
+-- Return the sequence generated by the given seed term
+function buildSeq (term)
+    local sequence = {}
+    repeat
+        table.insert(sequence, term)
+        if not nextTerm[term] then nextTerm[term] = findNext(term) end
+        term = nextTerm[term]
+    until contains(sequence, term)
+    return sequence
+end
+
+-- Main procedure
+nextTerm = {}
+local highest, seq, hiSeq = 0
+for i = 1, 10^6 do
+    seq = buildSeq(tostring(i))
+    if #seq > highest then
+        highest = #seq
+        hiSeq = {seq}
+    elseif #seq == highest then
+        table.insert(hiSeq, seq)
+    end
+end
+io.write("Seed values: ")
+for _, v in pairs(hiSeq) do io.write(v[1] .. " ") end
+print("\n\nIterations: " .. highest)
+print("\nSample sequence:")
+for _, v in pairs(hiSeq[1]) do print(v) end