Enumeration Problems (152)

Enumeration is a fundamental problem-solving technique in data structures and algorithms where you systematically try all possible candidates to find the correct solution. Often referred to as a controlled form of brute force, enumeration involves generating possibilities and checking which ones satisfy the problem’s constraints. While it may seem simple, enumeration becomes powerful when combined with pruning strategies and efficient data structures.

In coding interviews, enumeration problems frequently appear when the search space is manageable or when clever optimizations reduce the number of possibilities. Many interview questions begin with a naive enumeration approach and then improve performance using techniques such as Backtracking, Bitmask, or Recursion. Understanding how to enumerate possibilities efficiently helps you build intuition for more advanced algorithms.

Common enumeration patterns include:

• Generating all subsets, permutations, or combinations
• Trying every possible starting position or configuration
• Enumerating pairs, triplets, or subarrays in an Array
• Checking all candidate states before applying optimization techniques

Enumeration is particularly useful when constraints are small (for example, n ≤ 20), when the solution space can be pruned early, or when the problem requires exploring every valid configuration. Many classic interview problems—like subset generation, valid combinations, and exhaustive search tasks—start with enumeration before evolving into optimized solutions using Combinatorics or dynamic programming.

By practicing enumeration problems, you learn how to structure brute-force searches, recognize patterns in candidate generation, and optimize search spaces effectively. FleetCode provides 134 carefully curated Enumeration problems that help you master this essential interview technique and build the foundation for advanced algorithmic strategies.