Skip to content

Pattern Index

Complete reference for all 19 coding interview patterns. Use this to quickly identify which pattern applies to a problem.

Pattern Recognition Guide

# Pattern When to Use Key Signal Files Path
1 Two Pointers Sorted array, pair/triplet search, palindrome "sorted array", "pair that sums" coding-interview-patterns/{lang}/Two Pointers/
2 Hash Maps and Sets O(1) lookup, frequency counting, deduplication "find duplicate", "two sum unsorted" coding-interview-patterns/{lang}/Hash Maps and Sets/
3 Linked Lists In-place reversal, intersection, cycle "reverse linked list", "merge lists" coding-interview-patterns/{lang}/Linked Lists/
4 Fast and Slow Pointers Cycle detection, middle of list, happy number "detect cycle", "find middle" coding-interview-patterns/{lang}/Fast and Slow Pointers/
5 Sliding Windows Contiguous subarray/substring optimization "longest substring", "max sum subarray of size k" coding-interview-patterns/{lang}/Sliding Windows/
6 Binary Search Sorted data, minimize/maximize answer "sorted", "minimum time to", "find position" coding-interview-patterns/{lang}/Binary Search/
7 Stacks Matching brackets, monotonic relationships, undo "valid parentheses", "next greater" coding-interview-patterns/{lang}/Stacks/
8 Heaps Top-K, kth largest/smallest, merge K sorted "k largest", "median stream" coding-interview-patterns/{lang}/Heaps/
9 Intervals Overlapping ranges, merge, schedule "merge intervals", "meeting rooms" coding-interview-patterns/{lang}/Intervals/
10 Prefix Sums Range sum queries, subarray sum equals K "sum between indices", "subarray sum" coding-interview-patterns/{lang}/Prefix Sums/
11 Trees Hierarchical data, BST operations, traversal "binary tree", "lowest common ancestor" coding-interview-patterns/{lang}/Trees/
12 Tries Prefix matching, autocomplete, word search "starts with", "word dictionary" coding-interview-patterns/{lang}/Tries/
13 Graphs Connected components, shortest path, ordering "number of islands", "course schedule" coding-interview-patterns/{lang}/Graphs/
14 Backtracking Generate all combinations/permutations/subsets "all possible", "generate all" coding-interview-patterns/{lang}/Backtracking/
15 Dynamic Programming Overlapping subproblems, optimal substructure "minimum cost", "number of ways" coding-interview-patterns/{lang}/Dynamic Programming/
16 Greedy Local optimal leads to global optimal "minimum jumps", "maximum profit" coding-interview-patterns/{lang}/Greedy/
17 Sort and Search Custom ordering, multi-criteria sort "sort by", "kth element" coding-interview-patterns/{lang}/Sort and Search/
18 Bit Manipulation XOR tricks, power of 2, bit counting "single number", "count bits" coding-interview-patterns/{lang}/Bit Manipulation/
19 Math and Geometry GCD, modular arithmetic, matrix ops "rotate matrix", "GCD" coding-interview-patterns/{lang}/Math and Geometry/

Key Problems by Pattern

1. Two Pointers

  • pair_sum_sorted classic two-pointer convergence
  • triplet_sum sort + two pointers for 3Sum
  • largest_container container with most water

2. Hash Maps and Sets

  • pair_sum_unsorted hash map complement lookup
  • longest_chain_of_consecutive_numbers set-based union find
  • verify_sudoku_board multi-dimensional hash checking

3. Linked Lists

  • linked_list_reversal iterative pointer swap
  • linked_list_intersection two-pointer convergence
  • lru_cache hash map + doubly linked list

4. Fast and Slow Pointers

  • Cycle detection in linked list
  • Find middle node

5. Sliding Windows

  • longest_substring_with_unique_chars variable window + hash set
  • longest_uniform_substring_after_replacements variable window + frequency
  • find_the_insertion_index lower bound search
  • first_and_last_occurrences left/right bound binary search
  • find_the_target_in_a_rotated_sorted_array modified binary search

7. Stacks

  • evaluate_expression stack-based calculator
  • next_largest_number_to_the_right monotonic stack

8. Heaps

  • k_most_frequent_strings min-heap for top-K
  • median_of_an_integer_stream two heaps

9. Intervals

  • merge_overlapping_intervals sort + merge
  • largest_overlap_of_intervals sweep line

10–19

See the respective folders in coding-interview-patterns/cpp/ for the complete file list per pattern.

Language Coverage

Pattern C++ Python Go
Two Pointers ✅ 6 ✅ 6 ✅ 6
Hash Maps and Sets ✅ 8 ✅ 8 ✅ 8
Linked Lists ✅ 7 ✅ 7 ✅ 2
Sliding Windows ✅ 4 ✅ 4 ✅ 2
Binary Search ✅ 8 ✅ 8 ✅ 2
Stacks ✅ 6 ✅ 6 ✅ 2
Dynamic Programming ✅ 20 ✅ 20 ✅ 3
Graphs ✅ 11 ✅ 11 ✅ 3
Trees ✅ 14 ✅ 14 ✅ 2
Backtracking ✅ 5 ✅ 5 ✅ 2
Heaps ✅ 5 ✅ 5 ✅ 1
Greedy ✅ 3 ✅ 3 ✅ 1
Intervals ✅ 3 ✅ 3 ✅ 1
All others ✅ ✅ ❌