algorithm/tech-interview-handbook
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Tay Yang Shun
2017-09-20 15:27:28 +08:00
commit 2182a70770
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utilities/tree_traversal.py Normal file
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# Various iterative ways of traversing a tree.
def inorder_traversal(root):
"""
:type root: TreeNode
:rtype: List[int]
"""
if not root:
return []
result = []
stack = [root]
while len(stack) > 0:
curr_node = stack.pop()
if curr_node.left:
stack.append(curr_node)
stack.append(curr_node.left)
curr_node.left = None
else:
result.append(curr_node.val)
if curr_node.right:
stack.append(curr_node.right)
return result
def preorder_traversal(root):
"""
:type root: TreeNode
:rtype: List[int]
"""
if not root:
return []
result = []
stack = [root]
while len(stack) > 0:
curr_node = stack.pop()
result.append(curr_node.val)
if curr_node.right:
stack.append(curr_node.right)
if curr_node.left:
stack.append(curr_node.left)
return result
def postorder_traversal(root):
"""
:type root: TreeNode
:rtype: List[int]
"""
if not root:
return []
result = []
stack = [root]
while len(stack) > 0:
curr_node = stack.pop()
if curr_node.left:
stack.append(curr_node)
stack.append(curr_node.left)
curr_node.left = None
elif curr_node.right:
stack.append(curr_node)
stack.append(curr_node.right)
curr_node.right = None
else:
result.append(curr_node.val)
return result