Leetcode 218: The Skyline Problem

Leetcode 218: The Skyline Problem
The Skyline ProblemTotal Accepted:1071Total Submissions:6525

A city's skyline is the outer contour of the silhouette formed by all the buildings in that city when viewed from a distance. Now suppose you areGiven the locations and height of all the buildingsAs shown on a cityscape photo (Figure A), write a programOutput the skylineFormed by these buildings collectively (Figure B ).

The geometric information of each building is represented by a triplet of integers[Li, Ri, Hi], WhereLiAndRiAre the x coordinates of the left and right edge of the ith building, respectively, andHiIs its height. It is guaranteed that0 ≤ Li, Ri ≤ INT_MAX,0 < Hi ≤ INT_MAX, AndRi - Li > 0. You may assume all buildings are perfect rectangles grounded on an absolutely flat surface at height 0.

For instance, the dimensions of all buildings in Figure A are recorded: [ [2 9 10], [3 7 15], [5 12 12], [15 20 10], [19 24 8] ] .

The output is a list"Key points"(Red dots in Figure B) in the format[ [x1,y1], [x2, y2], [x3, y3], ... ]That uniquely defines a skyline.A key point is the left endpoint of a horizontal line segment. Note that the last key point, where the rightmost building ends, is merely used to mark the termination of the skyline, and always has zero height. also, the ground in between any two adjacent buildings shoshould be considered part of the skyline contour.

For instance, the skyline in Figure B shoshould be represented:[ [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 be in the range [0, 10000]. The input list is already sorted in ascending order by the left x position Li. The output list must be sorted by the x position. There must be 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 shoshould be merged into one in the final output as such: [...[2 3], [4 5], [12 7], ...]

[Idea]

Get up and write again :)

[CODE]

 

public class Solution {    public List
 
   getSkyline(int[][] buildings) {        List
  
    res = new ArrayList
   
    ();        PriorityQueue
    
      maxHeap = new PriorityQueue
     
      (11, new Comparator
      
       (){ @Override public int compare(Integer a, Integer b) { return b - a; } }); List
       
         bl = new ArrayList
        
         (); for(int i=0; i
         
          () { @Overridepublic int compare(int[] a, int[] b) { if(a[0]!=b[0]) return a[0] - b[0]; else return b[1] - a[1]; } }); int pre = 0, cur = 0; for(int i=0; i
          
           0) { maxHeap.add(b[1]); cur = maxHeap.peek(); } else { maxHeap.remove(-b[1]); cur = (maxHeap.peek()==null) ? 0 : maxHeap.peek(); } if(cur!=pre) { res.add(new int[]{b[0], cur}); pre = cur; } } return res; }}