Create skyline_problem.cpp

Author: avidLearnerInProgress

skyline_problem.cpp

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+logo
+
+218. The Skyline Problem
+Description
+Hints
+Submissions
+Discuss
+Solution
+      
+C++ T:O(nlogn)/S:O(n) with vector/multiset
+C++ T:O(nlogn)/S:O(n) with vector/multiset
+311
+VIEWS
+4
+Created at: November 30, 2020 12:00 PM
+
+HalleyWang
+HalleyWang
+ 59
+/*
+    sort x coord first, we will handle each point in x-increasing order.
+    For each building, we will have 2 points in our list, (L,H), (R,-H). Negative height means out of the building's width.
+    Maintain a priority queue to find out the current max y coord.
+    T:O(nlogn)/S:O(n)
+*/
+class Solution {
+public:
+    vector<vector<int>> getSkyline(vector<vector<int>>& buildings) 
+    {
+        vector<pair<int,int>> s;
+        multiset<int> q;
+        vector<vector<int>> ans;
+        for (auto building:buildings) {
+            s.push_back({building[0],building[2]});
+            s.push_back({building[1],-1*building[2]});
+        }
+        sort(s.begin(),s.end(),[](auto a, auto b){
+            if (a.first==b.first) return a.second>=b.second;
+            else return a.first<=b.first;
+        });
+        q.insert(0); int cur_max=0;
+        for (auto building:s) {
+            if (building.second<0) 
+                q.erase(q.find(-1*building.second));
+            else q.insert(building.second);
+            if (*(q.rbegin())!=cur_max) {
+                cur_max=*(q.rbegin());
+                ans.push_back({building.first,cur_max});
+            }
+        }
+        return ans;
+    }
+};