# Traversals of Binary Trees

I am trying to implement in-order, pre-order, and post-order traversals of a binary tree. My implementation seems to work for trees with a small number of nodes (as I have checked by hand) but the online software I am using says there are cases that my implementation fails (it does not provide the input that causes my implementation to fail). I have looked through several other threads on this site but cannot seem to find my mistake. Any hints or suggestions would be appreciated!

Note: "tree" is an array of nodes constructed using input data taken from the terminal (not shown).

```
class Node:
def __init__(self, key, left_child, right_child):
self.key = key
self.left_child = left_child
self.right_child = right_child
def in_order(self, root):
result = []
if root.left_child:
result.extend(self.in_order(tree[root.left_child]))
result.append(root.key)
if root.right_child:
result.extend(self.in_order(tree[root.right_child]))
return result
def pre_order(self, root):
result = []
result.append(root.key)
if root.left_child:
result.extend(self.pre_order(tree[root.left_child]))
if root.right_child:
result.extend(self.pre_order(tree[root.right_child]))
return result
def post_order(self, root):
result = []
if root.left_child:
result.extend(self.post_order(tree[root.left_child]))
if root.right_child:
result.extend(self.post_order(tree[root.right_child]))
result.append(root.key)
return result
```

Asked by:

**Emma298**| Posted: 06-12-2021

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