138 lines
3.4 KiB
Java
138 lines
3.4 KiB
Java
/**
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* Given n rectangular buildings in a 2-dimensional city, computes the skyline of these buildings,
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* eliminating hidden lines. The main task is to view buildings from a side and remove all sections
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* that are not visible.
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* Source for explanation: https://www.geeksforgeeks.org/the-skyline-problem-using-divide-and-conquer-algorithm/
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*/
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import java.util.ArrayList;
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import java.util.Iterator;
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import java.util.Scanner;
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public class SkylineProblem {
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Building[] building;
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int count;
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public void run() {
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Scanner sc = new Scanner(System.in);
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int num = sc.nextInt();
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this.building = new Building[num];
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for(int i = 0; i < num; i++) {
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String input = sc.next();
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String[] data = input.split(",");
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this.add(Integer.parseInt(data[0]), Integer.parseInt(data[1]), Integer.parseInt(data[2]));
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}
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this.print(this.findSkyline(0, num - 1));
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sc.close();
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}
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public void add(int left, int height, int right) {
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building[count++] = new Building(left, height, right);
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}
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public void print(ArrayList<Skyline> skyline) {
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Iterator<Skyline> it = skyline.iterator();
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while(it.hasNext()) {
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Skyline temp = it.next();
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System.out.print(temp.coordinates + "," + temp.height);
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if(it.hasNext()) {
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System.out.print(",");
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}
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}
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}
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public ArrayList<Skyline> findSkyline(int start, int end) {
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if(start == end) {
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ArrayList<Skyline> list = new ArrayList<>();
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list.add(new Skyline(building[start].left, building[start].height));
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list.add(new Skyline(building[end].right, 0));
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return list;
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}
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int mid = (start + end) / 2;
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ArrayList<Skyline> sky1 = this.findSkyline(start, mid);
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ArrayList<Skyline> sky2 = this.findSkyline(mid + 1, end);
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return this.mergeSkyline(sky1, sky2);
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}
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public ArrayList<Skyline> mergeSkyline(ArrayList<Skyline> sky1, ArrayList<Skyline> sky2) {
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int currentH1 = 0, currentH2 = 0;
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ArrayList<Skyline> skyline = new ArrayList<>();
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int maxH = 0;
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while(!sky1.isEmpty() && !sky2.isEmpty()) {
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if(sky1.get(0).coordinates < sky2.get(0).coordinates) {
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int currentX = sky1.get(0).coordinates;
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currentH1 = sky1.get(0).height;
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if(currentH1 < currentH2) {
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sky1.remove(0);
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if(maxH != currentH2) skyline.add(new Skyline(currentX, currentH2));
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} else {
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maxH = currentH1;
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sky1.remove(0);
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skyline.add(new Skyline(currentX, currentH1));
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}
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} else {
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int currentX = sky2.get(0).coordinates;
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currentH2 = sky2.get(0).height;
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if(currentH2 < currentH1) {
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sky2.remove(0);
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if(maxH != currentH1) skyline.add(new Skyline(currentX, currentH1));
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} else {
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maxH = currentH2;
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sky2.remove(0);
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skyline.add(new Skyline(currentX, currentH2));
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}
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}
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}
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while(!sky1.isEmpty()) {
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skyline.add(sky1.get(0));
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sky1.remove(0);
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}
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while(!sky2.isEmpty()) {
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skyline.add(sky2.get(0));
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sky2.remove(0);
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}
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return skyline;
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}
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public class Skyline {
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public int coordinates;
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public int height;
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public Skyline(int coordinates, int height) {
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this.coordinates = coordinates;
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this.height = height;
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}
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}
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public class Building {
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public int left;
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public int height;
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public int right;
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public Building(int left, int height, int right) {
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this.left = left;
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this.height = height;
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this.right = right;
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}
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}
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public static void main(String[] args) {
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SkylineProblem skylineProblem = new SkylineProblem();
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skylineProblem.run();
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}
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}
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