The Skyline Problem

// 超时class Solution {public:    vector<pair<int, int> > getSkyline(vector<vector<int>>& buildings) {        vector<pair<int, int> > r;        if (buildings.size() == 0) {            return r;        }        r.push_back(make_pair(buildings[0][0], buildings[0][2]));        set<int> tmp;        for (int i = 0; i < buildings.size(); ++i) {            tmp.insert(buildings[i][0]);            tmp.insert(buildings[i][1]);        }        set<int>::iterator a = tmp.begin();        set<int>::iterator b = ++a;        for (; b != tmp.end(); ++b, ++a) {            int max = 0;            for (int i = 0; i < buildings.size(); ++i) {                if (buildings[i][1] < *a) {                    continue;                }                if (buildings[i][0] > *b) {                    break;                }                max = max > buildings[i][2] ? max : buildings[i][2];            }            if (max != r.back().second) {                r.push_back(make_pair(*b, max));            }        }        return r;    }};