Added constant space solutions for populating next right pointers

Author: mingbowan

Populating Next Right Pointers in Each Node II.py

@@ -13,4 +13,21 @@ def connect(self, root):
                 if current[i].right is not None:
                     next.append(current[i].right)
             current = next
-        return root
+        return root
+
+    #### constant space solution
+    def connect_2(self, root):
+        if not root:
+            return
+        nexthead = root
+        while nexthead:
+            c, nexthead, prevs = nexthead, None, None
+            while c:
+                for x in [c.left, c.right]:
+                    if x:
+                        if not nexthead:
+                            nexthead, prevs = x, x
+                        else:
+                            prevs.next, prevs = x, x
+                c = c.next
+

Populating Next Right Pointers in Each Node.py

@@ -1,4 +1,5 @@
 class Solution:
+
     def connect(self, root):
         if root is None:
             return
@@ -7,4 +8,17 @@ def connect(self, root):
         if root.right and root.next:
             root.right.next = root.next.left
         self.connect(root.left)
-        self.connect(root.right)
+        self.connect(root.right)
+
+    # constant space solution
+    def connect_2(self, root):
+        head = root
+        while head:
+            current = head
+            while current:
+                if current.left:
+                    current.left.next = current.right
+                    if current.next:
+                        current.right.next = current.next.left
+                current = current.next
+            head = head.left