Leetcode:the Skyline problem

A city's skyline is the outer contour of the silhouette formed by all the buildings in then city then viewed from a Distan Ce. Now suppose you is given the locations and height of all the buildings as shown in a cityscape photo (figure A), write a Program to output the skyline formed by these buildings collectively (Figure B).the geometric information of each building was represented by a triplet of integers [Li, RI, Hi], where Li and Ri are T He x coordinates of the left and right edge of the ith building, respectively, and Hi are its height. It's Guaranteed that0≤li, Ri≤int_max, 0 < Hi≤int_max, and Ri-li > 0. Assume all buildings is perfect rectangles grounded on a absolutely flat surface at height 0. For instance, the dimensions of all buildings in Figure A is recorded as: [[2 9 10], [3 7 15], [5 12 12], [15 20 10], [19 24 8] ] . The output is a list of"Key Points"(Red dots in Figure B) in the format of [[X1,y1], [X2, Y2], [X3, Y3], ...] that uniquely defines a skyline. A key point was the left endpoint of a horizontal line segment. Note the last key point, where the rightmost building ends, was merely used to mark the termination of the skyline, an D always have zero height. Also, the ground in between any and adjacent buildings should is considered part of the Skyline Contour. For instance, the skyline in Figure B should is represented as:[[2 10], [3 15], [7 12], [12 0], [15 10], [20 8], [24, 0] ]. Notes:the number of buildings in any input list is guaranteed to being in the range [0, 10000]. The input list is already sorted on ascending order by the left X position li.the output list must being sorted by the X posi tion. There must is no consecutive horizontal lines of equal height in the output skyline. For instance, [... [2 3], [4 5], [7 5], [11 5], [12 7] ...] is not acceptable; The three lines of height 5 should is merged into one in theFinalOutput as such: [... [2 3], [4 5], [12 7], ...]

Reference to the Http://www.cnblogs.com/tonyluis/p/4564617.html

Don't understand why 16 lines are b[1]-a[1]

1  Public classSolution {2      Publiclist<int[]> Getskyline (int[] buildings) {3list<int[]> res =Newarraylist<int[]>();4Priorityqueue<integer> maxheap =NewPriorityqueue<integer> (11,NewComparator<integer>(){5              Public intCompare (integer A, integer b) {6                 returnB-A;7             }8         });9list<int[]> edges =Newarraylist<int[]>();Ten          for(int[] building:buildings) { OneEdges.add (New int[]{building[0], building[2]}); AEdges.add (New int[]{building[1],-building[2]}); -         } -Collections.sort (Edges,Newcomparator<int[]>() { the              Public intCompareint[] A,int[] b) { -                 returnA[0]==b[0]? B[1]-A[1]: a[0]-b[0]; -             } -         }); +          -         intCur=0, pre=0; +          for(int[] edge:edges) { A             if(Edge[1] > 0) { atMaxheap.add (edge[1]); -Cur =Maxheap.peek (); -             } -             Else { -Maxheap.remove (-edge[1]); -cur = maxheap.isempty ()? 0: Maxheap.peek (); in             } -             if(cur! =pre) { toRes.add (New int[]{edge[0], cur}); +Pre =cur; -             } the         } *          $         returnRes;Panax Notoginseng     } -}

Leetcode:the Skyline problem