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Invert Binary Tree

Invert a binary tree by swapping every left and right child, and return the root.

Answers use simple, clear English.

Time: O(n)Space: O(h)

Quick interview answer

Recursively swap children then invert subtrees (or BFS/DFS iteratively swapping at each node). Post-order or pre-order both work if you swap before/after consistently.

Detailed answer

Recursively swap children then invert subtrees (or BFS/DFS iteratively swapping at each node). Post-order or pre-order both work if you swap before/after consistently. Famous warm-up; interviewers often follow with serialize/deserialize.

Full explanation

Famous warm-up; interviewers often follow with serialize/deserialize.

Real example & use case

Mirroring a UI layout tree for RTL language support.

Pros & cons

Pros: O(n) clear. Cons: mutates in place — clone if immutability required.

Code example

def invert_tree(root):
    if not root:
        return None
    root.left, root.right = invert_tree(root.right), invert_tree(root.left)
    return root

Practice code · python (view only · no execution)

def invert_tree(root):
    if not root:
        return None
    root.left, root.right = invert_tree(root.right), invert_tree(root.left)
    return root

#tree#recursion