Recursion

Subtitle / Summary Invert Binary Tree looks tiny, but it is one of the fastest ways to test whether you really understand recursive structure on trees. This guide uses LeetCode 226 to break down the essence of “swap left and right subtrees”, covers both recursion and BFS, and shows how the same idea transfers to engineering scenarios. Reading time: 8-10 min Tags: Hot100, binary tree, recursion, BFS, tree transformation SEO keywords: Hot100, Invert Binary Tree, tree mirror, recursion, BFS, LeetCode 226 Meta description: Learn the recursive and BFS solutions for LeetCode 226, then extend the idea to layout mirroring and structural transformations. Target Readers Hot100 learners who want to verify whether they truly understand “apply recursion to every node in the whole tree” Developers who instinctively start traversing any tree problem, but are unsure when to process the current node Engineers who need tree mirroring, layout inversion, or symmetric structural transforms Background / Motivation The code for LeetCode 226 is usually very short, but the thinking pattern is extremely typical: ...

Subtitle / Summary “Maximum depth” is one of the cleanest starting points for tree recursion. Once you truly understand that the answer for the current tree depends on the answers from its left and right subtrees, a whole family of tree DP and DFS problems becomes easier. This guide uses LeetCode 104 to explain recursive DFS, level-order BFS, and the engineering value of the same pattern. Reading time: 9-11 min Tags: Hot100, binary tree, DFS, BFS, recursion SEO keywords: Hot100, Maximum Depth of Binary Tree, DFS, BFS, LeetCode 104 Meta description: Learn the DFS and BFS solutions for LeetCode 104 from the definition of depth, with engineering mappings and runnable multi-language code. Target Readers Learners who are just starting tree problems and want to truly internalize “tree recursion return values” Developers who can write traversals but get confused once the task becomes “compute height”, “compute path”, or “compute an answer” Engineers who need depth analysis on hierarchical data such as menus, org charts, or nested JSON Background / Motivation LeetCode 104 looks like an easy problem, but it is almost the parent problem of tree recursion: ...

Subtitle / Summary Reverse Linked List is the first serious pointer-rewiring exercise in Hot100. It looks simple, but most bugs come from broken links and wrong operation order. This ACERS guide explains the three-pointer iterative template thoroughly and compares it with recursion. Reading time: 10-12 min Tags: Hot100, linked list, pointer, iteration SEO keywords: Hot100, Reverse Linked List, three pointers, iterative, recursive, LeetCode 206 Meta description: Three-pointer iterative reversal in O(n)/O(1), with recursive contrast, common pitfalls, engineering mapping, and runnable multi-language implementations. Target Readers Hot100 learners and interview candidates Developers who often hit null-pointer or broken-chain bugs in list problems Engineers who want stable pointer manipulation patterns in C/C++/Rust/Go Background / Motivation In production code, “reverse linked list” may not appear as a LeetCode function, but the skill is highly transferable: ...