Dfs on Jeanphilo Blog

LeetCode 547: Number of Provinces, Turn an Adjacency Matrix into Connected Components

Fri, 29 May 2026 00:00:00 +0800

Turn LeetCode 547 Number of Provinces from direct connections in an adjacency matrix into connected component counting, then derive DFS, BFS, and Union Find solutions step by step.

LeetCode 78: Subsets, Derive the startIndex Backtracking Template

Sun, 03 May 2026 14:25:07 +0800

Problem Requirement

Input / Output

Input: nums, with 1 <= nums.length <= 10
Value range: -10 <= nums[i] <= 10
All elements in nums are distinct
Output: return all possible subsets of nums
Ordering: the result order does not matter, and subset element order is not the point

Example

Input: nums = [1,2,3]
Output: [[],[1],[2],[1,2],[3],[1,3],[2,3],[1,2,3]]

This tutorial builds one minimal Python solution.

Start From the Search Tree for `[1,2]`

The smallest branching example is:

Hot100: Binary Tree Maximum Path Sum (Tree DP / Single-Side Gain ACERS Guide)

Mon, 20 Apr 2026 10:01:46 +0800

A practical guide to LeetCode 124 covering the key design split: return only the best single-side gain upward, while using the full path through the current node to update a global answer.

Hot100: Diameter of Binary Tree (Tree DP / Height Return ACERS Guide)

Sun, 19 Apr 2026 15:51:55 +0800

A practical guide to LeetCode 543 covering the key split between returned height and global diameter updates, plus engineering mappings and runnable multi-language implementations.

Hot100: Lowest Common Ancestor of a Binary Tree (Postorder Return Semantics ACERS Guide)

Sun, 19 Apr 2026 15:51:55 +0800

A practical guide to LeetCode 236 covering the return-value meaning in postorder recursion, when the current node becomes the answer, and why a node can be its own ancestor.

Hot100: Validate Binary Search Tree (Range Constraints / Inorder ACERS Guide)

Sun, 19 Apr 2026 15:13:19 +0800

A practical guide to LeetCode 98 covering ancestor range constraints, why parent-only checks fail, and two stable solutions: recursive bounds and inorder validation.

LeetCode 216: Combination Sum III (Backtracking / Fixed-Length Search ACERS Guide)

Fri, 17 Apr 2026 14:31:12 +0800

Learn LeetCode 216 by deriving fixed-length combination search, use-once recursion, and bounded 1..9 pruning from the problem itself.

LeetCode 40: Combination Sum II (Backtracking / Same-Layer Dedup ACERS Guide)

Fri, 17 Apr 2026 14:31:10 +0800

Learn LeetCode 40 by deriving same-layer duplicate skipping, use-once recursion, and sorted pruning from the problem itself.

Hot100: Combination Sum (Backtracking / Pruning ACERS Guide)

Wed, 08 Apr 2026 16:22:57 +0800

A practical guide to LeetCode 39 that builds combination backtracking from scratch, explains remain-based state, and shows why sorting makes pruning safe.

Hot100: Permutations (used[] Backtracking ACERS Guide)

Fri, 03 Apr 2026 17:54:22 +0800

A practical guide to LeetCode 46 covering used[] state tracking, leaf-only collection, and runnable multi-language implementations.

LeetCode 133: Clone Graph Hash Map + DFS/BFS ACERS Guide

Thu, 19 Mar 2026 13:18:26 +0800

Clone a connected undirected graph by mapping original nodes to cloned nodes, with DFS and BFS variants, cycle handling, correctness reasoning, and runnable implementations in six languages.

Hot100: Binary Tree Level Order Traversal (BFS / DFS ACERS Guide)

Mon, 16 Mar 2026 13:00:56 +0800

A practical guide to LeetCode 102 covering level-by-level BFS, level-size boundaries, DFS depth buckets, and runnable multi-language implementations.

Hot100: Symmetric Tree (Mirror Recursion / BFS ACERS Guide)

Mon, 16 Mar 2026 13:00:55 +0800

A practical guide to LeetCode 101 covering mirror recursion, pairwise BFS checks, symmetry contracts, and runnable multi-language implementations.

Hot100: Same Tree (Synchronous Recursion / BFS ACERS Guide)

Mon, 16 Mar 2026 13:00:54 +0800

A practical guide to LeetCode 100 covering synchronous recursion, pairwise BFS validation, structural equivalence, and runnable multi-language implementations.

Hot100: Maximum Depth of Binary Tree (DFS / BFS ACERS Guide)

Fri, 06 Mar 2026 17:58:22 +0800

A practical guide to LeetCode 104 covering the depth definition, recursive DFS, level-order BFS, engineering mappings, and runnable multi-language implementations.

Hot100: Binary Tree Inorder Traversal (Recursion / Stack ACERS Guide)

Fri, 06 Mar 2026 17:58:21 +0800

A practical guide to LeetCode 94 covering left-root-right traversal, recursion, explicit stacks, engineering mappings, and runnable multi-language implementations.

Connected Components and Strongly Connected Components: Tarjan / Kosaraju ACERS Engineering Analysis

Mon, 09 Feb 2026 09:50:22 +0800

A systematic guide to undirected Connected Components and directed SCCs, with emphasis on Tarjan (common in production) and Kosaraju, mapped to graph-database scenarios such as community pre-grouping, subgraph splitting, and partition hints.

BFS / DFS Engineering Primer: k-hop Queries, Subgraph Extraction, and Path Existence ACERS Breakdown

Mon, 09 Feb 2026 09:44:11 +0800

Centered on three high-frequency graph tasks (k-hop query, subgraph extraction, and path existence), this article explains practical BFS/DFS iteration templates, early-stop pruning, and visited bitmap/bloom choices with runnable multi-language implementations.

Path Sum III: Prefix Sum + Hash Map Counting Downward Paths (LeetCode 437) ACERS Guide

Wed, 04 Feb 2026 16:02:26 +0800

Count downward paths in a binary tree whose sum equals targetSum in O(n) using prefix sums and a frequency hash map, with derivation, engineering mapping, and multi-language implementations.