Mastering the Merging of Overlapping Intervals in Python

A Comprehensive Guide to Efficiently Merging Overlapping Intervals Using Python

Mastering the Merging of Overlapping Intervals in Python


Merging overlapping intervals is a common problem in computer science, frequently encountered in tasks such as scheduling, calendar management, and data consolidation. The challenge lies in efficiently combining intervals that overlap, ensuring that all intervals are covered without redundancy.

In this article, we will explore a step-by-step solution to this problem using Python, optimizing for performance and accuracy.

Understanding the Problem

Given an array of intervals where intervals[i] = [start<sub>i</sub>, end<sub>i</sub>], merge all overlapping intervals, and return an array of the non-overlapping intervals that cover all the intervals in the input.

Example 1:

Input: intervals = [[1,3],[2,6],[8,10],[15,18]]
Output: [[1,6],[8,10],[15,18]]
Explanation: Since intervals [1,3] and [2,6] overlap, merge them into [1,6].

Example 2:

Input: intervals = [[1,4],[4,5]]
Output: [[1,5]]
Explanation: Intervals [1,4] and [4,5] are considered overlapping.


  • 1 <= intervals.length <= 10<sup>4</sup>

  • intervals[i].length == 2

  • 0 <= start<sub>i</sub> <= end<sub>i</sub> <= 10<sup>4</sup>

Initial Approach and Challenges

A naive approach to solving this problem might involve checking each pair of intervals for overlaps and merging them if necessary. However, this method is inefficient, especially for large datasets, as it involves multiple nested iterations. Thus, a more efficient algorithm is required.

Efficient Solution: Sorting and Merging

To merge overlapping intervals efficiently, we can follow these steps:

  1. Sort the Intervals: Start by sorting the list of intervals by their starting points. This simplifies the process of finding overlaps.

  2. Merge Intervals: Iterate through the sorted intervals and merge them if they overlap. If the current interval overlaps with the last merged interval, extend the last merged interval. Otherwise, add the current interval to the list of merged intervals.

Detailed Step-by-Step Solution in Python

Here's the Python code to achieve this:

from typing import List

def merge(intervals: List[List[int]]) -> List[List[int]]:
    if not intervals:
        return []

    # Sort the intervals based on the starting points
    intervals.sort(key=lambda x: x[0])

    merged_intervals = [intervals[0]]

    for current in intervals[1:]:
        last_merged = merged_intervals[-1]

        # If the current interval overlaps with the last merged interval, merge them
        if current[0] <= last_merged[1]:
            last_merged[1] = max(last_merged[1], current[1])
            # Otherwise, add the current interval to the merged list

    return merged_intervals

# Example 1
intervals1 = [[1, 3], [2, 6], [8, 10], [15, 18]]
print(merge(intervals1))  # Output: [[1, 6], [8, 10], [15, 18]]

# Example 2
intervals2 = [[1, 4], [4, 5]]
print(merge(intervals2))  # Output: [[1, 5]]

Time and Space Complexity Analysis

  • Time Complexity: The time complexity of this solution is O(n log n) due to the sorting step, where n is the number of intervals. The merging process itself takes O(n) time. Thus, the overall time complexity is dominated by the sorting step.

  • Space Complexity: The space complexity is O(n) in the worst case, where all intervals are added to the merged list without any overlaps.

Edge Cases and Testing

When implementing this solution, it's essential to consider and handle edge cases:

  1. Empty Input: If the input list is empty, the function should return an empty list.

  2. Single Interval: If there is only one interval, it should be returned as is.

  3. Fully Overlapping Intervals: Intervals that completely overlap should be merged into a single interval.

Practical Applications

Understanding how to merge overlapping intervals can be beneficial in various domains:

  • Calendar Management: Combining overlapping meeting times into a single time slot.

  • Data Consolidation: Merging overlapping data ranges in financial reports or log files.

  • Scheduling Tasks: Ensuring tasks are scheduled without conflicts in time slots.

FAQ Section

Q1: What is the primary benefit of sorting intervals before merging?

A1: Sorting intervals by their starting points simplifies the merging process, allowing us to efficiently identify and merge overlapping intervals in a single pass.

Q2: Can this algorithm be adapted for intervals with different types of data?

A2: Yes, the algorithm can be adapted for any type of data that can be compared and sorted based on their starting points.

Q3: How can we handle intervals represented in different formats?

A3: The algorithm can be adjusted to handle different interval formats by converting them into a standard format before processing.


Merging overlapping intervals is a fundamental problem with numerous practical applications. By leveraging sorting and efficient merging techniques, we can solve this problem optimally. The Python solution provided in this article ensures accurate results and optimal performance.

Practicing this solution and understanding its nuances can greatly benefit software engineers in handling real-world data consolidation tasks.

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