How to Fix Serialize and Deserialize Binary Tree Errors

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

Fix serialize and deserialize binary tree errors when null markers cause parsing failure or wrong tree shape.

Quick Fix

Wrong

def ser(r):
    if not r: return ''
    return str(r.val)+','+ser(r.left)+','+ser(r.right)

No null markers. Can't distinguish missing left vs right child.

Right

def ser(r):
    def dfs(n):
        if not n: return 'null'
        return str(n.val)+','+dfs(n.left)+','+dfs(n.right)
    return dfs(r)
def des(d):
    it=iter(d.split(','))
    def dfs():
        v=next(it)
        if v=='null': return None
        n=TreeNode(int(v)); n.left=dfs(); n.right=dfs()
        return n
    return dfs()

Input -> '1,2,null,null,3,4,null,null,5,null,null'. Restores original. O(n).

Prevention

Always include null markers. Use preorder. Iterator pattern for deserialization.

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