Count kth largest element in interval list
Last updated: February 13, 2026
Quick Overview
Given a list of intervals, each defined by a start and end point, your task is to find the k-th largest element among all the unique elements present in these intervals. The input will consist of a list of intervals and an integer k, and you should return the k-th largest unique element as an integer. If k is greater than the number of unique elements, return -1.
Citadel
February 13, 2026115
15
163 solved
Given a list of intervals, each defined by a start and end point, your task is to find the k-th largest element among all the unique elements present in these intervals. The input will consist of a list of intervals and an integer k, and you should return the k-th largest unique element as an integer. If k is greater than the number of unique elements, return -1.
This coding problem is frequently asked during Take-home Project at Citadel. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Citadel expects candidates to write production-quality code, not just solve the puzzle.
What the Interviewer Expects
- Identify the correct data structure and algorithm for the problem
- Write clean, bug-free code with proper variable naming
- Analyze time and space complexity correctly
- Handle basic edge cases (empty input, single element)
- Communicate your thought process while coding
Key Topics to Cover
How to Approach This
- Clarify input constraints and edge cases before writing code.
- Walk through your approach verbally and confirm with the interviewer before coding.
- Start with a brute force solution, then optimize. Mention time and space complexity.
- Test your solution with examples, including edge cases like empty input or duplicates.
- Consider common patterns: sliding window, two pointers, hash map, BFS/DFS, dynamic programming.
Possible Follow-up Questions
- How would your solution change if the input was sorted?
- Can you solve this in a single pass?
- How would you modify your solution to handle streaming input?
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Problem Analysis
To solve the problem of finding the k-th largest unique element among the intervals, we can utilize a combination of sorting and a data structure that facilitates unique value storage. The core patter...
Approach
- Extract Unique Elements: First, iterate through each interval and collect all the unique start and end points into a set. For example, given intervals
[(1, 3), (2, 5), (1, 2)], the unique ele...
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