How to Fix Postorder Binary Tree Traversal Errors

In this tutorial, you'll learn about How to Fix Postorder Binary Tree Traversal Errors. We cover key concepts, practical examples, and best practices.

Fix postorder binary tree traversal errors when child processing order reversed or visited flags mismanaged.

Quick Fix

Wrong

def postorder(r):
    if not r: return []
    return postorder(r.left)+postorder(r.right)+[r.val]

Stack overflow on deep trees.

Right

def postorder(r):
    res,st=[],[(r,False)]
    while st:
        cur,v=st.pop()
        if cur:
            if v: res.append(cur.val)
            else: st.append((cur,True)); st.append((cur.right,False)); st.append((cur.left,False))
    return res

Input: [1,null,2,3] -> [3,2,1]. Iterative with visited flag.

Prevention

Use visited flag to track if children processed. Process after both children done.

DodaTech Tools

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FAQ