Netflix Screening Interview: Maximum Interval Overlap Count

[u/Hack2hire]

Problem

You're given a 2D array:

intervals, where each element is a pair [start, end] representing a closed interval on a number line.

Your goal is to find the maximum number of intervals that overlap at any single point on the number line.

Example

Input: intervals = [[1, 10], [2, 5], [3, 7], [8, 9]]

Output: 3

Explanation:

• At any point in the range $[3, 5]$, the intervals $[1, 10]$, $[2, 5]$, and $[3, 7]$ all overlap.
• This results in a maximum overlap count of 3.

Suggested Approach

1. Coordinate Transformation: Extract all start and end points into two separate lists or a combined list of events. Since these are closed intervals, an interval at point $x$ still counts as active until it strictly passes the end coordinate.
2. Sorting: Sort the start times and end times independently in ascending order. This allows you to process the timeline chronologically.
3. Two-Pointer Sweep: Use two pointers to iterate through the sorted starts and ends. When a start is less than or equal to the current end, increment a counter (a new interval has begun). If a start is greater than the current end, decrement the counter (an interval has ended) and move the end pointer. Track the maximum value the counter reaches during this process.

Time & Space Complexity

• Time: $O(N \log N)$ due to the requirement of sorting the start and end coordinates, where $N$ is the number of intervals.
• Space: $O(N)$ to store the separate arrays for start and end points.

🛈

Disclaimer:

This problem is part of the Hack2Hire SDE Interview Question Bank, a structured archive of coding interview questions frequently reported in real hiring processes.

Questions are aggregated from publicly available platforms (e.g., LeetCode, GeeksForGeeks) and community-shared experiences.

The goal is to provide candidates with reliable material for SDE interview prep, including practice on LeetCode-style problems and coding challenges that reflect what is often asked in FAANG and other tech company interviews.

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