Tree Traversal Target: 10s
Preorder with null markers (#). Each node becomes: val, left_subtree, right_subtree. Null markers preserve structure.
def serialize(root):
res = []
def dfs(node):
if not node:
res.append('#')
return
res.append(str(node.val))
dfs(node.left)
dfs(node.right)
dfs(root)
return ','.join(res)Type it from memory. Go.