56. Merge Intervals

원문: https://doljae.tistory.com/260

[Merge Intervals - LeetCode

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leetcode.com](https://leetcode.com/problems/merge-intervals/)

양의 정수 2개로 이루어진 배열이 담긴 배열이 주어진다.

각 양의 정수는 시작과 끝을 의미하고 이 배열 하나를 interval로 한다.

만일 interval 간의 끝과 시작이 같거나 겹친다면 하나의 interval로 만들 수 있을 때 interval 들을 합친 결과를 반환하는 문제다.

예시

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].

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

1. 구현, Greedy(?)

from typing import *
from collections import deque

class Solution:
    def merge(self, intervals: List[List[int]]) -> List[List[int]]:
        intervals.sort()

        q = deque(intervals)
        answer = []

        while q:
            start, end = q.popleft()
            while q and end >= q[0][0]:
                end = max(end, q.popleft()[1])
            answer.append([start, end])

        return answer

2. 좀 더 정해에 가까운 구현

class Solution:
    def merge(self, intervals: List[List[int]]) -> List[List[int]]:
        start, end = [], []
        length = len(intervals)
        answer = []

        for interval in intervals:
            s, e = interval
            start.append(s)
            end.append(e)

        start.sort()
        end.sort()
        j = 0
        for i in range(length):
            if i == length - 1 or start[i + 1] > end[i]:
                answer.append([start[j], end[i]])
                j = i + 1

        return answer

설명은 아래 링크를 참고.

 [Beat 98% Java. Sort start & end respectively. - LeetCode Discuss

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leetcode.com](https://leetcode.com/problems/merge-intervals/discuss/21223/Beat-98-Java.-Sort-start-and-end-respectively./115420)

창의력 대장...

3. 트리로 구현

도 가능하나 가장 비효율적인 방법.