天际线问题（扫描线）

题目：https://leetcode-cn.com/problems/the-skyline-problem/ 代码：https://leetcode-cn.com/problems/the-skyline-problem/solution/218tian-ji-xian-wen-ti-sao-miao-xian-fa-by-ivan_al/

class Solution {
public:
    vector getSkyline(vector& buildings) {
        vector h;
        multiset m;
        vector res;

        //1、将每一个建筑分成“两个部分”，例如:[2,9,10]可以转换成[2，-10][9,10]，我们用负值来表示左边界
        for(const auto& b:buildings)
        {
            h.push_back({b[0], -b[2]});
            h.push_back({b[1], b[2]});
        }

        //2、根据x值对分段进行排序
        sort(h.begin(),h.end());
        int prev = 0, cur = 0;
        m.insert(0);

        //3、遍历
        for (auto i:h)
        {
            if (i.second