June 2018 Update

Task/Hailstone-sequence/Elena/hailstone-sequence.elena

@@ -0,0 +1,48 @@
+import system'collections.
+import extensions.
+
+int const maxNumber = 100000.
+
+Hailstone = (:n:lengths)
+[
+    if (n == 1)
+    [
+        ^ 1
+    ].
+
+    while (true)
+    [
+        if (lengths containsKey(n))
+        [
+            ^ lengths[n]
+        ];
+        [
+            if (n int; isEven)
+            [
+                lengths[n] := 1 + Hailstone(n/2, lengths)
+            ];
+            [
+                lengths[n] := 1 + Hailstone((3*n) + 1, lengths)
+            ]
+        ]
+    ]
+].
+
+program =
+[
+    int longestChain := 0.
+    int longestNumber := 0.
+    var recursiveLengths := Dictionary new.
+
+    1 till(maxNumber) do(:i)<int>
+    [
+        var chainLength := Hailstone(i, recursiveLengths).
+        if (longestChain < chainLength)
+        [
+               longestChain := chainLength.
+               longestNumber := i.
+        ]
+    ].
+
+    console printFormatted("max below {0}: {1} ({2} steps)", maxNumber, longestNumber, longestChain).
+].