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要用最大堆，是保证，最高的楼总能展现在最外面，那些矮的楼都被覆盖了。
循环中只要是左坐标，就要加入res中，只要这个左坐标还没有被用过，
想这个例子就好了：[2, 10], [3, 15], [5, 12], [7, 15]
遇到[5, 12]，这时peek出来的是15（因为这是最大堆），而15在上次循环中已经被用过，压入了res中，而12刚被压入，还没有结束，所以不能进入res。
public class Solution {public List<int[]> getSkyline(int[][] buildings) {List<int[]> res = new ArrayList<>();List<int[]> heights = new ArrayList<>();for (int[] b: buildings) {heights.add(new int[]{b[0], -b[2]});heights.add(new int[]{b[1], b[2]});}Collections.sort(heights, new Comparator<int[]>(){@Overridepublic int compare(int[] a, int[] b){if (a[0] != b[0]) {return a[0] - b[0];} else {return a[1] - b[1];}}});PriorityQueue<Integer> queue = new PriorityQueue<>(11, new Comparator<Integer>(){@Overridepublic int compare(Integer a, Integer b){return b - a;}});queue.offer(0);int prev = 0;for (int[] h: heights) {if (h[1] < 0) {queue.offer(-h[1]);} else {queue.remove(h[1]);}int cur = queue.peek();if (cur != prev) {res.add(new int[]{h[0], cur});prev = cur;}}return res;}
}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 are given the locations and height of all the buildings as shown on 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 is represented by a triplet of integers [Li, Ri, Hi], where Li and Ri are the x coordinates of the left and right edge of the ith building, respectively, and Hi is its height. It is guaranteed that 0 ≤ Li, Ri ≤ INT_MAX, 0 < Hi ≤ INT_MAX, and Ri - 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 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 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 should be considered part of the skyline contour.
For instance, the skyline in Figure B should be 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 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 should be merged into one in the final output as such:[...[2 3], [4 5], [12 7], ...]
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