LeetCode 792: Number of Matching Subsequences | Hash Map + Bucketing

Описание: Table of Contents:





Struggling with subsequence matching at scale? This Medium problem is a classic interview pattern — learn how to solve it efficiently using Hash Map bucketing instead of brute force repeated scanning.


🎯 Bucket each word by its current awaited character, then advance pointers using a single pass over the source string
🧠 Build intuition for why brute force fails at scale and how bucketing transforms O(n * m * k) into something far better
💻 Clean, readable CSharp implementation using arrays of queues or lists to represent buckets
📊 Full breakdown of time and space complexity and why this beats naive approaches in interviews
⚡ Watch for edge cases: empty words, duplicate words in the array, and characters not present in source at all


00:00 - Understanding problem statement
01:01 - Brute force approach
02:06 - Optimized solution
04:20 - Big O Notation explained
04:56 - Conclusion


⏱️ Time Complexity : O(S + sum of all word lengths), where S is the length of source
💾 Space Complexity : O(W) where W is the total number of words
📌 Difficulty : Medium
🔧 Technique : Hash Map Bucketing / Subsequence Pointer Advancement


1. LeetCode 392 – Is Subsequence (Easy)
2. LeetCode 524 – Longest Word in Dictionary through Deleting (Medium)
3. LeetCode 727 – Minimum Window Subsequence (Hard)
4. LeetCode 1023 – Camelcase Matching (Medium)


🔗 LeetCode Problem : https://leetcode.com/problems/number-...


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