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binary-search-tree-iterator.py
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binary-search-tree-iterator.py
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# Time: O(1)
# Space: O(h), h is height of binary tree
#
# 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.
#
# Definition for a binary tree node
class TreeNode:
def __init__(self, x):
self.val = x
self.left = None
self.right = None
class BSTIterator:
# @param root, a binary search tree's root node
def __init__(self, root):
self.stack = []
self.cur = root
# @return a boolean, whether we have a next smallest number
def hasNext(self):
return self.stack or self.cur
# @return an integer, the next smallest number
def next(self):
while self.cur:
self.stack.append(self.cur)
self.cur = self.cur.left
self.cur = self.stack.pop()
node = self.cur
self.cur = self.cur.right
return node.val
if __name__ == "__main__":
root = TreeNode(2)
root.left = TreeNode(1)
# Your BSTIterator will be called like this:
i, v = BSTIterator(root), []
while i.hasNext(): v.append(i.next())
print v