Preorder

Subtitle / Summary The key to LeetCode 105 is not memorizing that preorder and inorder can reconstruct a tree. It is understanding what each traversal contributes: preorder tells you the root, inorder tells you the left/right boundary. Once those roles are clear, the whole problem becomes a clean indexed divide-and-conquer. Reading time: 12-15 min Tags: Hot100, binary tree, divide and conquer, hash map, preorder SEO keywords: Construct Binary Tree from Preorder and Inorder Traversal, preorder, inorder, divide and conquer, hash map, LeetCode 105 Meta description: Learn LeetCode 105 from traversal roles, indexed recursion, and hash-map root lookup, with runnable multi-language implementations. A — Algorithm Problem Restatement Given the preorder traversal preorder and inorder traversal inorder of a binary tree, reconstruct the tree and return its root. ...

Subtitle / Summary The real difficulty of LeetCode 114 is not “flattening” a tree. It is rewiring pointers without destroying the structure you still need. Once you notice that the final linked list must follow preorder order, reverse preorder with a prev pointer becomes a very stable in-place solution. Reading time: 12-15 min Tags: Hot100, binary tree, preorder, in-place, recursion SEO keywords: Flatten Binary Tree to Linked List, preorder, in-place, reverse preorder, LeetCode 114 Meta description: Learn LeetCode 114 from preorder order and reverse-preorder rewiring, with step-by-step derivation, engineering mappings, and runnable multi-language implementations. A — Algorithm Problem Restatement Given the root root of a binary tree, flatten the tree into a linked list in place. ...