2016 Update

Task/Combinations/JavaScript/combinations-4.js

@@ -0,0 +1,46 @@
+(function (n) {
+
+  // n -> [a] -> [[a]]
+  function comb(n, lst) {
+    if (!n) return [[]];
+    if (!lst.length) return [];
+
+    var x = lst[0],
+      xs = lst.slice(1);
+
+    return comb(n - 1, xs).map(function (t) {
+      return [x].concat(t);
+    }).concat(comb(n, xs));
+  }
+
+  // f -> f
+  function memoized(fn) {
+    m = {};
+    return function (x) {
+      var args = [].slice.call(arguments),
+        strKey = args.join('-');
+
+      v = m[strKey];
+      if ('u' === (typeof v)[0])
+        m[strKey] = v = fn.apply(null, args);
+      return v;
+    }
+  }
+
+  // [m..n]
+  function range(m, n) {
+    return Array.apply(null, Array(n - m + 1)).map(function (x, i) {
+      return m + i;
+    });
+  }
+
+  var fnMemoized = memoized(comb),
+    lstRange = range(0, 4);
+
+  return fnMemoized(n, lstRange)
+
+  .map(function (x) {
+    return x.join(' ');
+  }).join('\n');
+
+})(3);