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SkylineProblem.java

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package Others;

import java.util.ArrayList;

import java.util.Iterator;

import java.util.Scanner;

public class SkylineProblem {

Building[] building;

int count;

public void run() {

Scanner sc = new Scanner(System.in);

int num = sc.nextInt();

this.building = new Building[num];

for (int i = 0; i < num; i++) {

String input = sc.next();

String[] data = input.split(",");

this.add(Integer.parseInt(data[0]), Integer.parseInt(data[1]), Integer.parseInt(data[2]));

}

this.print(this.findSkyline(0, num - 1));

sc.close();

}

public void add(int left, int height, int right) {

building[count++] = new Building(left, height, right);

}

public void print(ArrayList<Skyline> skyline) {

Iterator<Skyline> it = skyline.iterator();

while (it.hasNext()) {

Skyline temp = it.next();

System.out.print(temp.coordinates + "," + temp.height);

if (it.hasNext()) {

System.out.print(",");

}

}

}

public ArrayList<Skyline> findSkyline(int start, int end) {

if (start == end) {

ArrayList<Skyline> list = new ArrayList<>();

list.add(new Skyline(building[start].left, building[start].height));

list.add(new Skyline(building[end].right, 0));

return list;

}

int mid = (start + end) / 2;

ArrayList<Skyline> sky1 = this.findSkyline(start, mid);

ArrayList<Skyline> sky2 = this.findSkyline(mid + 1, end);

return this.mergeSkyline(sky1, sky2);

}

public ArrayList<Skyline> mergeSkyline(ArrayList<Skyline> sky1, ArrayList<Skyline> sky2) {

int currentH1 = 0, currentH2 = 0;

ArrayList<Skyline> skyline = new ArrayList<>();

int maxH = 0;

while (!sky1.isEmpty() && !sky2.isEmpty()) {

if (sky1.get(0).coordinates < sky2.get(0).coordinates) {

int currentX = sky1.get(0).coordinates;

currentH1 = sky1.get(0).height;

if (currentH1 < currentH2) {

sky1.remove(0);

if (maxH != currentH2) skyline.add(new Skyline(currentX, currentH2));

} else {

maxH = currentH1;

sky1.remove(0);

skyline.add(new Skyline(currentX, currentH1));

}

} else {

int currentX = sky2.get(0).coordinates;

currentH2 = sky2.get(0).height;

if (currentH2 < currentH1) {

sky2.remove(0);

if (maxH != currentH1) skyline.add(new Skyline(currentX, currentH1));

} else {

maxH = currentH2;

sky2.remove(0);

skyline.add(new Skyline(currentX, currentH2));

}

}

}

while (!sky1.isEmpty()) {

skyline.add(sky1.get(0));

sky1.remove(0);

}

while (!sky2.isEmpty()) {

skyline.add(sky2.get(0));

sky2.remove(0);

}

return skyline;

}

public class Skyline {

public int coordinates;

public int height;

public Skyline(int coordinates, int height) {

this.coordinates = coordinates;

this.height = height;

}

}

public class Building {

public int left;

public int height;

public int right;

public Building(int left, int height, int right) {

this.left = left;

this.height = height;

this.right = right;

}

}

public static void main(String[] args) {

SkylineProblem skylineProblem = new SkylineProblem();

skylineProblem.run();

}

}