Another update from ingydotnet^djgoku

Task/Hailstone-sequence/JavaScript/hailstone-sequence-4.js

@@ -0,0 +1,58 @@
+(function () {
+
+  function memoized(fn) {
+    var dctMemo = {};
+
+    return function (x) {
+      var varValue = dctMemo[x];
+
+      if ('u' === (typeof varValue)[0])
+        dctMemo[x] = varValue = fn(x);
+      return varValue;
+    };
+  }
+  // Hailstone Sequence
+  // n -> [n]
+  function hailstone(n) {
+    return n === 1 ? [1] : (
+      [n].concat(
+        hailstone(n % 2 ? n * 3 + 1 : n / 2)
+      )
+    )
+  }
+
+   // Derived a memoized version of the function,
+  //  which can reuse previously calculated paths
+
+  var fnCollatz = memoized(hailstone);
+
+  // Iterative version of range
+  // [m..n]
+  function range(m, n) {
+    var a = Array(n - m + 1),
+      i = n + 1;
+    while (i--) a[i - 1] = i;
+    return a;
+  }
+
+  // Fold/reduce over an array to find the maximum length
+  function longestBelow(n) {
+    return range(1, n).reduce(
+      function (a, x, i) {
+        var lng = fnCollatz(x).length;
+
+        return lng > a.l ? {
+          n: i + 1,
+          l: lng
+        } : a
+
+      }, {
+        n: 0,
+        l: 0
+      }
+    )
+  }
+
+  return longestBelow(100000);
+
+})();