The Skyline Problem Leetcode Java__Java

public class Solution {  class KeyPoint {        public int key;        public int height;        public KeyPoint next = null;        public KeyPoint(int key, int height) {            this.key = key;            this.height = height;        }    }    public static int[] getKeyPoint(int key, int height) {        int[] kp = new int[2];        kp[0] = key;        kp[1] = height;        return kp;    }    public List<int[]> getSkyline(int[][] buildings) {        KeyPoint head = new KeyPoint(-1,0);        KeyPoint prevKP = head;        for (int[] building:buildings) {            int l = building[0], r = building[1], h= building[2];            // insert left point            while (prevKP.next != null && prevKP.next.key <= l) prevKP = prevKP.next;            int preHeight = prevKP.height;            if (prevKP.key == l) prevKP.height = Math.max(prevKP.height, h);            else if (prevKP.height < h) {                KeyPoint next = prevKP.next;                prevKP.next = new KeyPoint(l, h);                prevKP = prevKP.next;                prevKP.next = next;            }            // insert right point and update points in between            KeyPoint prev = prevKP, cur = prevKP.next;            while (cur != null && cur.key < r) {                preHeight = cur.height;                cur.height = Math.max(cur.height, h);                if (cur.height == prev.height)                    prev.next = cur.next;                else                    prev = cur;                cur = cur.next;            }            if (prev.height != preHeight && prev.key != r && (cur == null || cur.key != r)) {                KeyPoint next = prev.next;                prev.next = new KeyPoint(r, preHeight);                prev.next.next = next;            }        }        // convert to List<int[]>        List<int[]> list = new ArrayList<int[]>();        KeyPoint prev = head, cur = head.next;        while (cur != null) {            if (cur.height != prev.height)                list.add(getKeyPoint(cur.key, cur.height));            prev = cur;            cur = cur.next;        }        return list;    }}