Coding Interview Patterns — All 21…

  13M 2H 

Sliding Window

Efficiently process subarrays or substrings of a fixed or variable size.

Finding max/min subarray of size k
Longest substring without repeating characters

15 problems Study pattern

 5E 7M 1H 

Two Pointers

Use two indices moving toward each other or in the same direction to solve linear problems.

Pair sum in sorted array
Removing duplicates in-place

13 problems Study pattern

 1E 7M 2H 

Binary Search

Halve the search space each step to find an element or boundary in O(log n).

Searching in sorted array
Finding first/last occurrence

10 problems Study pattern

 3E 4M  

Prefix Sum

Precompute cumulative sums to answer range queries in O(1).

Range sum queries
Subarray sum equals k

7 problems Study pattern

 6E 6M  

Hash Map / Set

Trade space for time using O(1) lookup to find pairs, duplicates, and frequencies.

Two sum (find complement)
Anagram grouping

12 problems Study pattern

 1E 9M  

Stack

LIFO structure for matching brackets, evaluating expressions, and monotonic problems.

Valid parentheses / bracket matching
Next greater element

10 problems Study pattern

  9M 1H 

Queue / BFS

Level-by-level traversal for shortest paths and layer-based problems.

Shortest path in unweighted graph
Level-order tree traversal

10 problems Study pattern

  7M 2H 

Heap / Priority Queue

Efficiently track the k-th largest/smallest element or merge sorted sequences.

Kth largest/smallest element
Merge k sorted lists

9 problems Study pattern

 4E 6M 1H 

Linked List

Pointer manipulation for in-place list operations without extra memory.

Detecting cycles (Floyd's algorithm)
Reversing a linked list

11 problems Study pattern

 4E 10M 2H 

Trees / DFS

Recursive and iterative depth-first traversal for tree structure problems.

Tree height/depth
Path sum problems

16 problems Study pattern

9M

Graphs

DFS and BFS on adjacency lists for connectivity, cycles, and path problems.

Number of islands
Clone graph

9 problems Study pattern

 3E 21M 2H 

Dynamic Programming

Break problems into overlapping subproblems and build up solutions bottom-up.

Fibonacci and climbing stairs
Knapsack variants

26 problems Study pattern

  7M 1H 

Greedy

Make the locally optimal choice at each step to achieve a globally optimal solution.

Jump game
Gas station

8 problems Study pattern

  9M 1H 

Backtracking

Explore all possibilities recursively, pruning invalid branches early.

Generate all permutations/combinations/subsets
N-Queens

10 problems Study pattern

  4M 1H 

Trie

Prefix tree for efficient string search, autocomplete, and word matching.

Implement Trie (insert/search/startsWith)
Word search II

5 problems Study pattern

  5M 1H 

Union Find

Disjoint set union for grouping, connectivity, and cycle detection.

Number of connected components
Redundant connection (cycle detection)

6 problems Study pattern

 1E 4M 1H 

Monotonic Stack

Maintain a sorted stack to find next/previous greater or smaller elements in O(n).

Largest rectangle in histogram
Trapping rain water

6 problems Study pattern

4M

Topological Sort

Linear ordering of vertices in a DAG — essential for dependency problems.

Course Schedule (detect cycle)
Course Schedule II (ordering)

4 problems Study pattern

 6E 2M  

Bit Manipulation

Use bitwise operations to solve XOR, subset, and number theory problems.

Single number (XOR trick)
Number of 1 bits (Hamming weight)

8 problems Study pattern

 1E 2M 1H 

Intervals

Merge, insert, and count overlapping intervals after sorting by start time.

Merge intervals
Insert interval

4 problems Study pattern

 1E 6M  

Matrix

Navigate 2D grids with DFS/BFS, rotation, spiral traversal, and flood fill.

Rotate image 90°
Spiral matrix traversal

7 problems Study pattern