Binary Search Tree Iterator

Implement an iterator over a binary search tree (BST). Your iterator is initialized with the root node of a BST.

Calling would return the next smallest number in the next() BST.

Note: next() hasNext() and should run in average O (1) time and uses O (h) memory, where H is the height of the Tree.

Ideas:

The result is saved to a queue by the middle sequence traversal, hasnext () determines whether the queue is empty, GetNext () returns the queue header element to

1  Public classBstiterator {2     PrivateQueue<integer> Queueofinorder =NewLinkedlist<integer> ();//to save a queue that is traversed by a sequence3      Publicbstiterator (TreeNode root) {4Inorder (root);//Middle Sequence traversal tree, get middle sequence traversal node queue5     }6 7     /** @returnwhether we have a next smallest number*/8      Public BooleanHasnext () {9         if(Queueofinorder.isempty ())Ten             return false;//The queue is empty, indicating that the last element has been One         return true; A     } -  -     /** @returnThe next smallest number*/ the      Public intNext () { -Integer Headofqueue =Queueofinorder.poll (); -          -         returnHeadofqueue; +     } -      +     /** A * Middle sequence traversal tree at      */ -     Private voidinorder (TreeNode root) { -         if(NULL!=root) { - inorder (root.left); - Queueofinorder.add (root.val); - inorder (root.right); in         } -     } to}

Binary Search Tree Iterator