Mock Coding Interview: Find First and Last Position (Binary Search)
Watch a full mock coding interview where the candidate tackles LeetCode 34: Find First and Last Position of Element in Sorted Array — one of the most common binary search questions asked in technical interviews at top tech companies.
This coding interview covers the full problem-solving arc from initial approach through debugging and optimization. The candidate identifies that a modified binary search is needed to find both the lower and upper bounds of a target element in O(log n) time. You'll see how they work through the tricky edge cases that trip up most candidates — particularly the off-by-one errors in boundary conditions and the key insight of tracking a "candidate" index during the search.
0:00 Introduction and first question
1:30 Binary search approach and complexity analysis
4:00 Coding the initial solution
6:00 Second question: Find first and last position of element
8:30 Modified binary search for lower bound
12:00 Pseudocode walkthrough and edge case discussion
15:00 Interviewer hint: candidate lower bound technique
19:00 Writing the actual code with helper function
25:00 Testing with hand-traced examples
30:00 Debugging off-by-one boundary errors
35:00 Fixing the while loop termination condition
39:00 Running all test cases
41:30 Interviewer feedback and performance review
Problem: LeetCode 34 — Find First and Last Position of Element in Sorted Array: https://leetcode.com/problems/find-fi...
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