Add week 7 solutions : reorderList

Author: yolophg

reorder-list/yolophg.js

@@ -0,0 +1,27 @@
+// Time Complexity: O(n)
+// Space Complexity: O(n)
+
+var reorderList = function (head) {
+  // push all nodes onto a stack.
+  let stack = [];
+  let current = head;
+  while (current) {
+    stack.push(current);
+    current = current.next;
+  }
+
+  // reorder the list.
+  let n = stack.length;
+  current = head;
+
+  for (let i = 0; i < Math.floor(n / 2); i++) {
+    let next = current.next;
+    let last = stack.pop();
+
+    current.next = last;
+    last.next = next;
+    current = next;
+  }
+  // ensure the last node points to null.
+  if (current) current.next = null;
+};