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Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST.
Calling next()
will return the next smallest number in the BST.
Note: next()
and hasNext()
should run in average O(1) time and uses O(h) memory, where h is the height of the tree.
Credits:
Special thanks to @ts for adding this problem and creating all test cases.
Answer:
# Definition for a binary tree node
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class BSTIterator(object):
def dfs(self,node):
if node==None:
return
left=node.left
right=node.right
self.dfs(left)
self.nodelist.append(node)
self.dfs(right)
def __init__(self, root):
"""
:type root: TreeNode
"""
self.nodelist=[]
self.dfs(root)
self.pos=0
def hasNext(self):
"""
:rtype: bool
"""
if self.pos<len(self.nodelist):
return True
return False
def next(self):
"""
:rtype: int
"""
result=self.nodelist[self.pos].val
self.pos+=1
return result
# Your BSTIterator will be called like this:
# i, v = BSTIterator(root), []
# while i.hasNext(): v.append(i.next())
inoder traversal