Backtracking

Subtitle / Summary If Subsets teaches the skeleton of combination-style backtracking, Permutations teaches the core of state-based backtracking: at each position, choose one unused element, continue until the path length reaches n, and only then collect the answer. Reading time: 10-12 min Tags: Hot100, backtracking, permutations, DFS SEO keywords: Permutations, backtracking, used array, DFS, LeetCode 46 Meta description: Learn the stable permutation backtracking template for LeetCode 46, with state recovery, engineering analogies, and runnable multi-language solutions. Target Readers Hot100 learners who have already finished 78. Subsets and want the next backtracking template Developers who understand recursion but still make mistakes when restoring state Engineers who need to enumerate execution orders, test sequences, or ordering-sensitive plans Background / Motivation The key difference between combinations and permutations is simple: ...

Subtitle / Summary Subsets is the cleanest entry point into Hot100 backtracking. The main thing to stabilize is not “enumerate everything”, but the three invariants behind the template: path, startIndex, and “every node is already a valid answer”. Reading time: 10-12 min Tags: Hot100, backtracking, subsets, DFS SEO keywords: Subsets, backtracking, startIndex, power set, LeetCode 78 Meta description: Learn the stable backtracking template for LeetCode 78, with engineering analogies, pitfalls, and runnable multi-language solutions. Target Readers Hot100 learners starting the backtracking block today Developers who can write DFS but still mix up combinations and permutations Engineers who need to enumerate feature sets, candidate policies, or configuration bundles Background / Motivation Many “real” problems reduce to a subset model: ...