DSA Patterns · Week 6–7

Validate Binary Search Tree

01 / 13Present00:00

DSA Patterns • Week 6–7

01 / 13

Validate Binary Search Tree

Almost every tree problem is DFS returning information upward, or BFS by levels.

StackShade deck

Predict → explain → retrieve

COURSE CONTENTS

Validate Binary Search Tree

01How This Journey WorksDay 0 · 4 topics0/4

Why pattern-based learning beats grinding8 min Set up your mistakes log + template notebook10 min Your spaced revision calendar (Day 1 / 3 / 7 / 21)6 min Big-O intuition builder: visualize growth rates15 min

02Complexity, Arrays & HashingWeek 1–2 · 11 topics0/11

Big-O, time & space complexity crash course20 min Interactive: watch hashing turn Two Sum from O(n²) to O(n)10 min Two Sum10 min Contains Duplicate5 min Valid Anagram10 min Group Anagrams15 min Top K Frequent Elements20 min Product of Array Except Self25 min Valid Sudoku20 min Longest Consecutive Sequence30 min Write your Arrays & Hashing template from memory15 min

03Two PointersWeek 2–3 · 7 topics0/7

Two Pointers pattern: opposite-end vs same-direction12 min Valid Palindrome10 min Two Sum II (sorted)10 min 3Sum25 min Container With Most Water20 min Trapping Rain Water35 min Template + mistakes log review15 min

04Sliding WindowWeek 3–4 · 8 topics0/8

Sliding Window: fixed vs dynamic windows12 min Interactive: window expand/shrink visualizer10 min Best Time to Buy & Sell Stock10 min Longest Substring Without Repeating Characters15 min Longest Repeating Character Replacement25 min Permutation in String25 min Minimum Window Substring35 min Sliding Window Maximum (deque)30 min

05StackWeek 4 · 8 topics0/8

Stack pattern + the monotonic stack superpower12 min Valid Parentheses10 min Min Stack15 min Evaluate Reverse Polish Notation15 min Generate Parentheses20 min Daily Temperatures20 min Car Fleet25 min Largest Rectangle in Histogram35 min

06Binary SearchWeek 5 · 8 topics0/8

Binary Search beyond sorted arrays: search on the answer space15 min Binary Search (classic)5 min Search a 2D Matrix15 min Koko Eating Bananas20 min Find Minimum in Rotated Sorted Array20 min Search in Rotated Sorted Array25 min Time Based Key-Value Store20 min Median of Two Sorted Arrays40 min

07Linked ListWeek 5–6 · 10 topics0/10

Linked List mechanics: dummy nodes, runner technique12 min Reverse Linked List10 min Merge Two Sorted Lists15 min Linked List Cycle10 min Reorder List20 min Remove Nth Node From End15 min Copy List with Random Pointer25 min LRU Cache35 min Merge K Sorted Lists30 min Reverse Nodes in K-Group35 min

08TreesWeek 6–7 · 13 topics0/13

DFS vs BFS mental models + BST properties15 min Interactive: tree traversal visualizer15 min Invert Binary Tree5 min Maximum Depth5 min Diameter of Binary Tree15 min Balanced Binary Tree15 min Same Tree / Subtree of Another Tree20 min Lowest Common Ancestor of BST15 min Binary Tree Level Order Traversal15 min Validate Binary Search Tree20 min Kth Smallest Element in BST20 min Construct Tree from Preorder & Inorder30 min Serialize & Deserialize Binary Tree35 min

09TriesWeek 7 · 4 topics0/4

Trie structure: nodes, children maps, end-of-word flags10 min Implement Trie (Prefix Tree)20 min Design Add & Search Words Data Structure25 min Word Search II40 min

10Heap / Priority QueueWeek 8 · 8 topics0/8

Heaps: min/max, push/pop in O(log n), heapify in O(n)12 min Kth Largest Element in a Stream15 min Last Stone Weight10 min K Closest Points to Origin15 min Kth Largest Element in an Array20 min Task Scheduler30 min Design Twitter30 min Find Median from Data Stream35 min

11BacktrackingWeek 8–9 · 11 topics0/11

Backtracking template: the choose-explore-unchoose loop12 min Interactive: subsets decision-tree visualizer10 min Subsets15 min Combination Sum20 min Permutations20 min Subsets II (duplicates)20 min Combination Sum II25 min Word Search25 min Palindrome Partitioning30 min Letter Combinations of a Phone Number20 min N-Queens40 min

12GraphsWeek 9–10 · 17 topics0/17

Graph representations + BFS/DFS templates15 min Interactive: BFS ripple on a grid10 min Number of Islands15 min Clone Graph20 min Max Area of Island15 min Pacific Atlantic Water Flow30 min Surrounded Regions25 min Rotting Oranges20 min Course Schedule I & II (topo sort)30 min Graph Valid Tree20 min Number of Connected Components20 min Redundant Connection (Union-Find)25 min Word Ladder35 min Network Delay Time (Dijkstra)30 min Cheapest Flights Within K Stops (Bellman-Ford)30 min Swim in Rising Water35 min Alien Dictionary40 min

131-D Dynamic ProgrammingWeek 10–11 · 14 topics0/14

DP thinking: overlapping subproblems + optimal substructure18 min Interactive: memoization table filling live10 min Climbing Stairs10 min Min Cost Climbing Stairs10 min House Robber15 min House Robber II20 min Longest Palindromic Substring25 min Palindromic Substrings20 min Decode Ways25 min Coin Change25 min Maximum Product Subarray20 min Word Break25 min Longest Increasing Subsequence30 min Partition Equal Subset Sum30 min

142-D Dynamic ProgrammingWeek 11–12 · 11 topics0/11

2-D DP: grid paths and sequence alignment15 min Unique Paths15 min Longest Common Subsequence25 min Best Time to Buy & Sell Stock with Cooldown25 min Coin Change II25 min Target Sum30 min Interleaving String30 min Edit Distance35 min Distinct Subsequences35 min Burst Balloons40 min Regular Expression Matching40 min

15Greedy, Intervals & BitsWeek 12 · 12 topics0/12

Greedy intuition + when it fails12 min Maximum Subarray (Kadane's)15 min Jump Game I & II25 min Gas Station20 min Hand of Straights20 min Merge Intervals20 min Insert Interval15 min Non-overlapping Intervals20 min Meeting Rooms I & II25 min Single Number (XOR)10 min Number of 1 Bits / Counting Bits15 min Reverse Bits / Missing Number / Sum of Two Integers25 min

16Mock Interviews & Mixed RevisionWeek 13 · 6 topics0/6

Timed mock set 1: 2 mediums in 45 min (mixed patterns)45 min Timed mock set 2: 1 easy + 1 hard in 50 min50 min Timed mock set 3: graphs + DP mix50 min Rewrite all 16 pattern templates from memory60 min Mistakes log: re-solve every logged problem90 min Spaced revision sweep: Day 21 recall for all patterns45 min