Coding Interview Patterns

Coding interview patterns are strategies or approaches used to solve common types of problems encountered in technical interviews. Familiarizing yourself with these patterns can significantly enhance your problem-solving efficiency. Here are some key patterns often seen in coding interviews:

1. Sliding Window

  • Used For: Problems involving contiguous subarrays or substrings, like finding the longest substring with no repeating characters.
  • Key Concept: Dynamically adjust the start and end of a window to satisfy certain conditions.

2. Two Pointers

  • Used For: Array and linked list problems, such as reversing an array or finding a pair that sums up to a target.
  • Key Concept: Using two pointers, which could move towards each other or in the same direction, to efficiently solve problems without extra space.

3. Fast and Slow Pointers

  • Used For: Detecting cycles in a linked list, finding the middle element of a list.
  • Key Concept: Two pointers moving at different speeds to solve problems in a single pass.

4. Divide and Conquer

  • Used For: Complex problems that can be broken down into smaller sub-problems, like merge sort or quick sort.
  • Key Concept: Divide the problem into sub-problems, solve them independently, and then combine the results.

5. Dynamic Programming

  • Used For: Problems requiring optimization over time, like finding the longest increasing subsequence or the minimum path sum.
  • Key Concept: Storing the results of sub-problems to avoid redundant work.

6. Backtracking

  • Used For: Problems where you need to find all possible solutions, like permutations of a string or solving a Sudoku.
  • Key Concept: Explore each possibility and backtrack to try a different path if a dead end is reached.

7. Breadth-First Search (BFS)

  • Used For: Traversing trees or graphs level by level, like finding the shortest path in a maze.
  • Key Concept: Use a queue to process nodes level by level.

8. Depth-First Search (DFS)

  • Used For: Exploring all paths or combinations in a tree or graph, like finding all leaf nodes.
  • Key Concept: Use recursion or a stack to explore paths to their fullest before backtracking.

9. Greedy Algorithms

  • Used For: Problems where local optimization leads to a global solution, like finding the minimum number of coins for change.
  • Key Concept: Choose the best option at the current moment without considering the bigger picture.

10. Binary Search

  • Used For: Searching in a sorted array or finding an element satisfying certain conditions.
  • Key Concept: Repeatedly divide the search interval in half to find the target.

11. Segment Trees

  • Used For: Problems requiring range queries and modifications over an array, like finding the sum or minimum in a range.
  • Key Concept: A tree data structure that allows storing information about array segments, enabling efficient queries and updates.

12. Topological Sort (Graphs)

  • Used For: Problems involving dependencies, like course scheduling or build system ordering.
  • Key Concept: Sort nodes in a directed graph in a linear order where for every directed edge from node A to B, A comes before B.

13. Union-Find (Disjoint Set)

  • Used For: Problems involving grouping or connecting components, like finding connected components in a graph.
  • Key Concept: A data structure that keeps track of elements partitioned into disjoint sets and supports union and find operations.

14. Interval Merging

  • Used For: Problems involving overlapping intervals, like merging meeting times.
  • Key Concept: Merge overlapping intervals to produce a set of mutually exclusive intervals.

15. Heap (Priority Queue)

  • Used For: Problems requiring constant access to the minimum or maximum element, like finding the Kth largest element.
  • Key Concept: A binary tree-based data structure that maintains the heap property (min-heap or max-heap).

16. Trie (Prefix Tree)

  • Used For: Problems involving string manipulation, like autocomplete features or word searches.
  • Key Concept: A tree-like data structure that stores a dynamic set of strings where each node represents a character of a string.

17. Kadane's Algorithm (Dynamic Programming)

  • Used For: Finding the maximum sum subarray in an array.
  • Key Concept: Dynamic programming approach to keep track of the maximum sum of subarrays ending at different positions.

18. Floyd's Tortoise and Hare (Cycle Detection)

  • Used For: Detecting cycles in a sequence or linked list.
  • Key Concept: Use two pointers moving at different speeds to determine whether a cycle exists.

19. Suffix Array and Suffix Tree

  • Used For: Advanced string problems, like finding the longest repeated substring.
  • Key Concept: Data structures that provide efficient ways to handle queries related to substrings. Suffix arrays are a space-efficient version of suffix trees.

20. Bucket Sort / Counting Sort

  • Used For: Sorting problems where the input is uniformly distributed over a range.
  • Key Concept: Sort elements by distributing them into a number of buckets and then sorting these buckets individually.


Each of these patterns offers a unique approach to solving complex problems and can be particularly effective for certain types of questions in coding interviews. Understanding and practicing these patterns can significantly enhance your problem-solving skills and improve your performance in technical interviews.

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