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218.java
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218.java
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public class Solution {
public List<int[]> getSkyline(int[][] buildings) {
List<int[]> ret = new ArrayList<>();
if(buildings == null || buildings.length == 0) return ret;
// List of time Series
List<Integer> time = new ArrayList<>();
// list of events, values is index of buildings.
Map<Integer, List<Integer>> events = new HashMap<>();
// heap of highest building,
PriorityQueue<int[]> pq = new PriorityQueue<int[]> (new Comparator<int[]>() {
@Override
public int compare(int[]o1, int[]o2) {
return o2[2] - o1[2];
}
});
for(int i =0; i<buildings.length; ++i) {
int[] cur = buildings[i];
if(!events.containsKey(cur[0])) {
events.put(cur[0], new ArrayList<Integer>());
time.add(cur[0]);
}
if(!events.containsKey(cur[1])) {
events.put(cur[1], new ArrayList<Integer>());
time.add(cur[1]);
}
events.get(cur[0]).add(i);
}
Collections.sort(time);
for(int i=0; i< time.size(); ++i) {
int cur = time.get(i);
List<Integer> curEvent = events.get(cur);
for(Integer j : curEvent) {
pq.add(buildings[j]);
}
int h = 0;
while(!pq.isEmpty()) {
int[] curHigh = pq.peek();
if(curHigh[1] <= cur) {
pq.poll();
continue;
}
h = curHigh[2];
break;
}
if(ret.size() == 0 || ret.get(ret.size() - 1)[1] != h) {
ret.add(new int[]{cur, h});
}
}
return ret;
}
}