Greedy on interval list
Last updated: January 15, 2026
Quick Overview
Given a list of intervals, write a function to select the maximum number of non-overlapping intervals that can be attended. Each interval is represented as a pair of integers [start, end], and your function should return the count of the maximum number of non-overlapping intervals that can be selected. The input will be a list of intervals, and the output should be an integer representing the maximum count.
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Given a list of intervals, write a function to select the maximum number of non-overlapping intervals that can be attended. Each interval is represented as a pair of integers [start, end], and your function should return the count of the maximum number of non-overlapping intervals that can be selected. The input will be a list of intervals, and the output should be an integer representing the maximum count.
Coding interviews at Pinterest focus on problem-solving approach as much as the final solution. The interviewer wants to see you break down the problem, consider edge cases, and optimize iteratively. Communication throughout the process is key.
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
- Can you solve this in a single pass?
- How would you modify your solution to handle streaming input?
- Can you solve this iteratively instead of recursively (or vice versa)?
- What if the input doesn't fit in memory?
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Problem Analysis
This problem can be effectively solved using a greedy algorithm approach. The key insight is that to maximize the number of non-overlapping intervals, we should always choose the interval that ends th...
Approach
- Sort the Intervals: Start by sorting the list of intervals based on their end times. For example, given intervals
[[1,2], [2,3], [3,4], [1,3]], the sorted order will be `[[1,2], [1,3], [2,3],...
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