LeetCode-in-All

56. Merge Intervals

Medium

Given an array of intervals where intervals[i] = [starti, endi], 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] overlaps, 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.

Constraints:

• 1 <= intervals.length <= 104
• intervals[i].length == 2
• 0 <= starti <= endi <= 104

Here are the steps to solve the task using the Solution class:

1. Define the Solution class with a method named merge that takes in a list of intervals.
2. Inside the merge method, sort the intervals based on their start times.
3. Initialize an empty list called merged_intervals to store the merged intervals.
4. Iterate through the sorted intervals.
5. For each interval, if the merged_intervals list is empty or if the current interval’s start time is greater than the end time of the last interval in the merged_intervals list, append the current interval to merged_intervals.
6. Otherwise, merge the current interval with the last interval in the merged_intervals list by updating the end time of the last interval if the current interval’s end time is greater.
7. After iterating through all intervals, return the merged_intervals list.

Here’s the implementation:

from typing import List

class Solution:
    def merge(self, intervals: List[List[int]]) -> List[List[int]]:
        intervals.sort(key=lambda x: x[0])
        merged_intervals = []
        
        for interval in intervals:
            if not merged_intervals or interval[0] > merged_intervals[-1][1]:
                merged_intervals.append(interval)
            else:
                merged_intervals[-1][1] = max(merged_intervals[-1][1], interval[1])
        
        return merged_intervals

# Example usage:
intervals1 = \[\[1, 3], [2, 6], [8, 10], [15, 18]]
intervals2 = \[\[1, 4], [4, 5]]

sol = Solution()
print(sol.merge(intervals1))  # Output: [[1, 6], [8, 10], [15, 18]]
print(sol.merge(intervals2))  # Output: [[1, 5]]

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