Flatten a binary tree into a linked list (preorder traversal)?

Short answer: TreeNode prev = null; void Flatten(TreeNode root) { if (root == null) return; Flatten(root.right); Flatten(root.left); root.right = prev; root.left = null; prev = root; } Explanation: Postorder traversal (right-left-root) to flatten tree in place.

Example code

TreeNode prev = null; void Flatten(TreeNode root) { if (root == null) return; Flatten(root.right); Flatten(root.left); root.right = prev;
root.left = null;
prev = root;
} Explanation: Postorder traversal (right-left-root) to flatten tree in place.

Real-world example (ShopNest)

In coding rounds, state complexity aloud, write a clear ShopNest-flavored example (orders, carts), then handle edge cases (empty list, null, overflow).

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.