Mock Coding Interview: Combination Sum (Backtracking)
Watch a full mock coding interview where the candidate tackles Combination Sum, one of the most popular backtracking problems in coding interviews (LeetCode 39). This 55-minute session covers two problems and includes real-time problem solving, debugging, and interviewer feedback.
The interview starts with a warm-up problem (Unique Paths on an MxN grid using dynamic programming), then moves into the main challenge: given a list of candidate numbers and a target, find all unique combinations that sum to the target. The candidate first builds a brute-force solution that generates all combinations and filters by sum, then works through extending the solution to allow using the same number multiple times. The interviewer guides the candidate toward a cleaner recursive backtracking approach where at each index you branch between including or skipping a number. The session covers Python implementation, edge case testing, and complexity analysis.
0:00 Introduction and language selection (Python)
0:10 Warm-up problem: Unique Paths on MxN grid (dynamic programming)
1:33 Problem 2 introduction: Combination Sum
2:03 Reading problem statement and examples
3:08 Clarifying questions (duplicates, positive numbers, sorted input)
4:49 Discussing brute-force approach
6:29 Exploring sliding window idea and why it fails
7:31 Brute-force: generate all combinations, filter by sum
9:36 Complexity discussion for brute-force approach
11:11 Coding the combination generator (recursive)
17:06 Coding the match/filter function
18:27 Writing test cases and debugging
21:43 Verifying output against expected results
25:23 Extending to allow repeated candidates
28:10 Approach discussion for repeated elements
33:47 Interviewer guides toward full recursive backtracking
39:10 Implementing recursive backtracking approach
45:08 Space complexity discussion
51:17 Feedback and interview tips
54:31 Closing discussion on problem difficulty
Problem links:
Combination Sum (LeetCode 39): https://leetcode.com/problems/combina...
Unique Paths (LeetCode 62): https://leetcode.com/problems/unique-...
Auf dieser Seite können Sie das Online-Video Mock Coding Interview: Combination Sum (Backtracking) mit der Dauer stunde minuten sekunde in guter Qualität ansehen, das der Benutzer abrar 20 Mai 2019 hochgeladen hat, den Link mit Freunden und Bekannten teilen, dieses Video wurde auf Youtube bereits 2,841 Mal angesehen und es wurde von 15 den Zuschauern gefallen. Viel Spaß beim Betrachtenden Zuschauern gefallen!
