Leetcode 218:the Skyline problem

The Skyline problemTotal Accepted: 1071 Total Submissions: 6525

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 isgiven the locations and height of all the buildings as shown in a cityscape photo (figure a), Write a program tooutput the skyline formed by these buildings collectively (Figure B).

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The geometric information of each building was represented by a triplet of integers [Li, Ri, Hi] , where and is the Li Ri x Co Ordinates of the left and right edge of the ith building, respectively, and are its Hi height. It's guaranteed that 0 ≤ 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 that [ [x1,y1], [x2, y2], [x3, y3], ... ] uniquely defines a skyline . A keypoint 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 all input list is guaranteed to being in the range [0, 10000] .
• The input list is already sorted in ascending order by the left X position Li .
• The output list must is sorted by the X position.
• There must is no consecutive horizontal lines of equal height in the output skyline. For instance, was not [...[2 3], [4 5], [7 5], [11 5], [12 7]...] acceptable; The three lines of height 5 should being merged into one in the final output as such:[...[2 3], [4 5], [12 7], ...]

Ideas

Get up and write again:)

[CODE]

public class Solution {public list<int[]> getskyline (int[][] buildings) {list<int[]> res = new ARR        Aylist<int[]> (); priorityqueue<integer> maxheap = new Priorityqueue<integer> (one, new comparator<integer> () {@O            Verride public int Compare (integer A, integer b) {return b-a;        }        });        list<int[]> bl = new arraylist<int[]> ();                for (int i=0; i<buildings.length; i++) {int[] b = buildings[i];            Bl.add (New int[]{b[0], b[2]});        Bl.add (New int[]{b[1],-b[2]});  } collections.sort (BL, new comparator<int[]> () {@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<bl.size (); i++) {int[] b = bl.get (i); if (b[1]>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; }}

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Leetcode 218:the Skyline problem