Leetcode 上的题
Topcoder tutorial:
some from gitbook about sweep line problems on leetcode:
https://robinliu.gitbooks.io/leetcode/content/Sweep_Line.html
面经：
题1：
Given an array of intervals in a line consisting of start and end points[[s1,e1],[s2,e2],...] (si < ei), find any point that is covered by mostintervals.code:
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
/**
* Given an array of intervals in a line consisting of start and end points
* [[s1,e1],[s2,e2],...] (si < ei), find any point that is covered by most
* intervals.
*/
public class IntervalCover {
public static class Interval {
int start;
int end;
Interval(int start, int end) {
this.start = start;
this.end = end;
}
}
public int getDensity(List<Interval> intervals) {
int[] starts = new int[intervals.size()];
int[] ends = new int[intervals.size()];
for (int i = 0; i < starts.length; i++) {
starts[i] = intervals.get(i).start;
ends[i] = intervals.get(i).end;
}
Arrays.sort(starts);
Arrays.sort(ends);
int end = 0;
int ans = 0;
for (int i = 0; i < starts.length; i++) {
if (starts[i] >= ends[end]) {
end++;
} else {
ans = starts[i];
}
}
return ans;
}
public static void main(String[] args) {
// String input = "[[0,30],[5,10],[15,20]]";
// String input = "[[7,10],[2,4]]";
// String input = "[[5,8],[6,8]]";
// String input = "[[13,15],[1,13]]";
String input = "[[2,7]]";
List<Interval> intervals = new ArrayList<Interval>();
for (String str : input.substring(2, input.length() - 2).split("\\],\\[")) {
String[] strs = str.split(",");
intervals.add(new Interval(Integer.valueOf(strs[0]), Integer.valueOf(strs[1])));
}
System.out.println(new IntervalCover().getDensity(intervals));
}
}
题2：
Given an array of rectangles consisting of left top and right down points[[x1,y1, x2, y2],[x3,y3,x4,y4],...] , find any point that is covered by mostrectangles.
public class IntervalD2 {
public static class Rectangle {
int x1;
int y1;
int x2;
int y2;
Rectangle(int x1, int y1, int x2, int y2) {
this.x1 = x1;
this.x2 = x2;
this.y1 = y1;
this.y2 = y2;
}
@Override
public String toString() {
return x1 + "|" + y1 + "|" + x2 + "|" + y2;
}
}
public int[] getArea(List<Rectangle> rects) {
Set<Integer> ys = new HashSet<Integer>();
Map<Integer, List<Rectangle>> map = new HashMap<Integer, List<Rectangle>>();
for (Rectangle rect : rects) {
ys.add(rect.y1);
ys.add(rect.y2);
List<Rectangle> list = map.getOrDefault(rect.y1, new ArrayList<>());
list.add(rect);
map.put(rect.y1, list);
list = map.getOrDefault(rect.y2, new ArrayList<>());
list.add(rect);
map.put(rect.y2, list);
}
List<Integer> yList = new ArrayList<Integer>(ys);
Collections.sort(yList);
PriorityQueue<Rectangle> pq = new PriorityQueue<Rectangle>((o1, o2) -> Integer.compare(o1.y2, o2.y2));
int ans = 0;
int ans_x = 0;
int ans_y = 0;
for (int y : yList) {
List<Rectangle> list = map.get(y);
if (list == null) {
continue;
}
for (Rectangle rect : list) {
if (rect.y1 == y) {
pq.add(rect);
}
}
int[] starts = new int[pq.size()];
int[] ends = new int[pq.size()];
int counter = 0;
System.out.println(pq.toString());
for (Rectangle rect : pq) {
starts[counter] = rect.x1;
ends[counter++] = rect.x2;
}
Arrays.sort(starts);
Arrays.sort(ends);
int r = 0;
int index = 0;
int pos = 0;
for (int i = 0; i < starts.length; i++) {
if (starts[i] < ends[index]) {
r++;
pos = ends[index];
} else {
index++;
}
}
if (r > ans) {
ans = r;
ans_x = pos;
ans_y = y;
}
while (!pq.isEmpty() && pq.peek().y2 <= y) {
pq.poll();
}
}
return new int[] {ans_x, ans_y, ans};
}
public static void main(String[] args) {
String input = "[[1,1,4,4],[3,3,4,4],[2,4,6,6],[7,7,8,8]]";
List<Rectangle> rects = new ArrayList<Rectangle>();
for (String rect : input.substring(2, input.length() - 2).split("\\],\\[")) {
String[] strs = rect.split(",");
rects.add(new Rectangle(Integer.valueOf(strs[0]), Integer.valueOf(strs[1]), Integer.valueOf(strs[2]), Integer.valueOf(strs[3])));
}
System.out.println(Arrays.toString(new IntervalD2().getArea(rects)));
}
}
题3：
Given an array of rectangles consisting of left top and right down points[[x1,y1, x2, y2],[x3,y3,x4,y4],...] , find the area covered by all these rectangles.
import com.sun.scenario.effect.impl.state.LinearConvolveKernel;
import java.util.*;
/**
*
*/
public class IntervalD2 {
public static class Rectangle {
int x1;
int y1;
int x2;
int y2;
Rectangle(int x1, int y1, int x2, int y2) {
this.x1 = x1;
this.x2 = x2;
this.y1 = y1;
this.y2 = y2;
}
@Override
public String toString() {
return x1 + "|" + y1 + "|" + x2 + "|" + y2;
}
}
public int getArea2(List<Rectangle> rects) {
int ans = 0;
Set<Integer> ys = new HashSet<Integer>();
Map<Integer, List<Rectangle>> map = new HashMap<Integer, List<Rectangle>>();
for (Rectangle rect : rects) {
ys.add(rect.y1);
ys.add(rect.y2);
List<Rectangle> list = map.getOrDefault(rect.y1, new ArrayList<>());
list.add(rect);
map.put(rect.y1, list);
list = map.getOrDefault(rect.y2, new ArrayList<>());
list.add(rect);
map.put(rect.y2, list);
}
System.out.println(map.toString());
List<Integer> yList = new ArrayList<Integer>(ys);
Collections.sort(yList);
System.out.println(yList.toString());
PriorityQueue<Rectangle> pq = new PriorityQueue<Rectangle>((o1, o2) -> Integer.compare(o1.y2, o2.y2));
for (int i = 0; i < yList.size(); i++) {
int y = yList.get(i);
List<Rectangle> list = map.get(y);
if (list == null) {
continue;
}
System.out.println(pq.toString());
if (!pq.isEmpty()) {
int[] starts = new int[pq.size()];
int[] ends = new int[pq.size()];
int counter = 0;
int deltaY = yList.get(i) - yList.get(i - 1);
for (Rectangle rect : pq) {
starts[counter] = rect.x1;
ends[counter++] = rect.x2;
}
Arrays.sort(starts);
Arrays.sort(ends);
int a = 0;
int b = 0;
int r = 0;
while (a < starts.length) {
if (starts[a] < ends[b]) {
if (r == 0) {
ans += (ends[b] - starts[a]) * deltaY;
System.out.println("ans: " + ans);
}
a++;
r++;
} else {
r--;
b++;
}
}
while (!pq.isEmpty() && pq.peek().y2 == y) {
pq.poll();
}
}
for (Rectangle rect : list) {
if (rect.y1 == y) {
pq.add(rect);
}
}
}
return ans;
}
public static void main(String[] args) {
String input = "[[1,1,4,4],[3,3,4,4],[4,4,6,6],[7,7,8,8]]";
List<Rectangle> rects = new ArrayList<Rectangle>();
for (String rect : input.substring(2, input.length() - 2).split("\\],\\[")) {
String[] strs = rect.split(",");
rects.add(new Rectangle(Integer.valueOf(strs[0]), Integer.valueOf(strs[1]), Integer.valueOf(strs[2]), Integer.valueOf(strs[3])));
}
System.out.println(new IntervalD2().getArea2(rects));
}
}
时间： 2024-10-20 08:19:42