1586. Binary Search Tree Iterator II
Last updated
Last updated
https://leetcode.com/problems/binary-search-tree-iterator-ii
Implement the BSTIterator
class that represents an iterator over the in-order traversal of a binary search tree (BST):
BSTIterator(TreeNode root)
Initializes an object of the BSTIterator
class. The root
of the BST is given as part of the constructor. The pointer should be initialized to a non-existent number smaller than any element in the BST.
boolean hasNext()
Returns true
if there exists a number in the traversal to the right of the pointer, otherwise returns false
.
int next()
Moves the pointer to the right, then returns the number at the pointer.
boolean hasPrev()
Returns true
if there exists a number in the traversal to the left of the pointer, otherwise returns false
.
int prev()
Moves the pointer to the left, then returns the number at the pointer.
Notice that by initializing the pointer to a non-existent smallest number, the first call to next()
will return the smallest element in the BST.
You may assume that next()
and prev()
calls will always be valid. That is, there will be at least a next/previous number in the in-order traversal when next()
/prev()
is called.
Example 1:
Constraints:
The number of nodes in the tree is in the range [1, 105]
.
0 <= Node.val <= 106
At most 105
calls will be made to hasNext
, next
, hasPrev
, and prev
.
Follow up: Could you solve the problem without precalculating the values of the tree?