Two-pointer technique

"When you need to find a pair or compare from both ends, two pointers walking towards each other are your best friends"

Practice: 3Sum (LC 15) Two Sum II (LC 167)

Sliding window

"When you need to track a running sequence or subarray of fixed/variable size, slide a window like checking dirt on a glass pane"

Practice: Longest Substring (LC 3) Character Replacement (LC 424)

Array manipulations

"Think of array elements as cards in a deck - you can shuffle, rotate, or rearrange them based on patterns"

Practice: Rotate Array (LC 189) Move Zeroes (LC 283)

String manipulations

"Strings are just arrays with special powers - you can slide, compare, or build them character by character"

Practice: Palindromic Substring (LC 5) Palindromic Substrings (LC 647)

Single Linked List

"Like a treasure hunt where each node gives you the clue to find the next one"

Practice: Reverse List (LC 206) Merge Lists (LC 21)

Double Linked List

"When you need to walk both forward and backward, like browsing history in a web browser"

Practice: LRU Cache (LC 146) Flatten List (LC 430)

Stack & Queue Operations

"Think of stacking plates - last in, first out - perfect for matching brackets or tracking history"

Practice: Valid Parentheses (LC 20) Min Stack (LC 155)

Tree Traversals

"Different ways to read a family tree - preorder, inorder, postorder"

Practice: Inorder Traversal (LC 94) Postorder Traversal (LC 145)

BST Operations

"Every node is a gatekeeper - smaller values go left, larger values go right"

Practice: Validate BST (LC 98) Insert into BST (LC 701)

Hash Tables

"Like a library index - gives you direct access to what you're looking for"

Practice: Two Sum (LC 1) Group Anagrams (LC 49)

Heaps

"A family tree where parents are always larger (or smaller) than their children"

Practice: Median Finder (LC 295) Merge K Lists (LC 23)

BFS & DFS

"Explore a maze level by level (BFS) or as deep as possible (DFS)"

Practice: Number of Islands (LC 200) Clone Graph (LC 133)

Shortest Path

"Like Google Maps finding the quickest route between two points"

Practice: Network Delay (LC 743) Cheapest Flights (LC 787)

Basic Concepts

"Write down results you've already calculated - don't solve the same math problem twice"

Practice: Climbing Stairs (LC 70) Coin Change (LC 322)

Advanced Patterns

"Most DP problems are variations of either choosing/not choosing items"

Practice: House Robber (LC 198) LIS (LC 300)

Greedy Algorithms

"Always pick what looks best right now"

Practice: Merge Intervals (LC 56) Jump Game II (LC 45)

Bit Manipulation

"Working with individual bits is like flipping switches on or off"

Practice: Number of 1 Bits (LC 191) Counting Bits (LC 338)

Amity ServiceNow DSA Preparation Roadmap