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Add iteration version (#322)

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Gini5 2019-02-09 09:54:07 +08:00 committed by Ashwek Swamy
parent c6be53e1c4
commit faf16d7ced
1 changed files with 56 additions and 2 deletions
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58
traversals/binary_tree_traversals.py
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@ -46,7 +46,6 @@ def build_tree():
node_found.right = right_node node_found.right = right_node
q.put(right_node) q.put(right_node)
def pre_order(node): def pre_order(node):
if not isinstance(node, TreeNode) or not node: if not isinstance(node, TreeNode) or not node:
return return
@ -54,7 +53,6 @@ def pre_order(node):
pre_order(node.left) pre_order(node.left)
pre_order(node.right) pre_order(node.right)
def in_order(node): def in_order(node):
if not isinstance(node, TreeNode) or not node: if not isinstance(node, TreeNode) or not node:
return return
@ -84,6 +82,50 @@ def level_order(node):
if node_dequeued.right: if node_dequeued.right:
q.put(node_dequeued.right) q.put(node_dequeued.right)
#iteration version
def pre_order_iter(node):
if not isinstance(node, TreeNode) or not node:
return
stack = []
n = node
while n or stack:
while n: #start from root node, find its left child
print(n.data, end=" ")
stack.append(n)
n = n.left
#end of while means current node doesn't have left child
n = stack.pop()
#start to traverse its right child
n = n.right
def in_order_iter(node):
if not isinstance(node, TreeNode) or not node:
return
stack = []
n = node
while n or stack:
while n:
stack.append(n)
n = n.left
n = stack.pop()
print(n.data, end=" ")
n = n.right
def post_order_iter(node):
if not isinstance(node, TreeNode) or not node:
return
stack1, stack2 = [], []
n = node
stack1.append(n)
while stack1: #to find the reversed order of post order, store it in stack2
n = stack1.pop()
if n.left:
stack1.append(n.left)
if n.right:
stack1.append(n.right)
stack2.append(n)
while stack2: #pop up from stack2 will be the post order
print(stack2.pop().data, end=" ")
if __name__ == '__main__': if __name__ == '__main__':
print("\n********* Binary Tree Traversals ************\n") print("\n********* Binary Tree Traversals ************\n")
@ -104,3 +146,15 @@ if __name__ == '__main__':
print("\n********* Level Order Traversal ************") print("\n********* Level Order Traversal ************")
level_order(node) level_order(node)
print("\n******************************************\n") print("\n******************************************\n")
print("\n********* Pre Order Traversal - Iteration Version ************")
pre_order_iter(node)
print("\n******************************************\n")
print("\n********* In Order Traversal - Iteration Version ************")
in_order_iter(node)
print("\n******************************************\n")
print("\n********* Post Order Traversal - Iteration Version ************")
post_order_iter(node)
print("\n******************************************\n")