56. Merge Intervals

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] 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.

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# https://leetcode.com/problems/merge-intervals/description/

'''
1. 아이디어 :
    1)  정렬을 하고, 각 구간을 비교하여 겹치는 구간을 합친다.
2. 시간복잡도 :
    1)   O(nlogn) + O(n) = O(nlogn)
    -   정렬 시간 + 탐색 시간
3. 자료구조 :
    1)  List
'''


class Solution:
    def merge(self, intervals: List[List[int]]) -> List[List[int]]:
        intervals.sort(key = lambda x : x[0])
        print(intervals)
        ans = [intervals[0]]
        for i in range(1, len(intervals)):
            if intervals[i][0] <= ans[-1][1]:
                ans[-1][1] = max(ans[-1][1], intervals[i][1])
            else:
                ans.append(intervals[i])
        return ans