Sweep Line
391. Number of Airplanes in the Sky
https://www.lintcode.com/problem/number-of-airplanes-in-the-sky/description?_from=ladder&&fromId=4
思路:将起飞时间和降落时间放到同一个数组中, 标识出是起飞还是降落时间, 然后对数组排序,遍历数组即可, 碰到起飞计数器加一, 碰到降落计数器减一. 维护最大值作为答案.
注意降落优先于起飞 可通过flag标记降落为0 上升为1,保证按time相等按flag排序降落为先
/**
* Definition of Interval:
* public classs Interval {
* int start, end;
* Interval(int start, int end) {
* this.start = start;
* this.end = end;
* }
* }
*/ class Point{
int time;
int flag; Point(int t, int s) {
this.time = t;
this.flag = s;
}
public static Comparator<Point> PointComparator = new Comparator<Point>() {
public int compare(Point p1, Point p2) {
if(p1.time == p2.time)
return p1.flag - p2.flag;
else
return p1.time - p2.time;
}
};
} public class Solution {
/**
* @param airplanes: An interval array
* @return: Count of airplanes are in the sky.
*/
public int countOfAirplanes(List<Interval> airplanes) {
// write your code here
List<Point> list = new ArrayList<>(airplanes.size()*2);
for(Interval i:airplanes){
list.add(new Point(i.start,1));
list.add(new Point(i.end,-1));
} Collections.sort(list,Point.PointComparator);
int count=0,ans =1;
for(Point p:list){
if(p.flag==1)
count++;
else
count--; ans = Math.max(ans,count);
} return ans; }
}
919. Meeting Rooms II
https://www.lintcode.com/problem/meeting-rooms-ii/description?_from=ladder&&fromId=4
/**
* Definition of Interval:
* public classs Interval {
* int start, end;
* Interval(int start, int end) {
* this.start = start;
* this.end = end;
* }
* }
*/
class Meeting{
int time;
int flag;
public Meeting(int time,int flag){
this.time = time;
this.flag = flag;
} public static Comparator<Meeting> comparator = new Comparator<Meeting>(){
@Override
public int compare(Meeting m1, Meeting m2){
if(m1.time==m2.time){
return m1.flag - m2.flag;
}
return m1.time-m2.time;
}
};
}
public class Solution {
/**
* @param intervals: an array of meeting time intervals
* @return: the minimum number of conference rooms required
*/
public int minMeetingRooms(List<Interval> intervals) {
// Write your code here
if(intervals == null || intervals.size()==0){
return 0;
} List<Meeting> meetings = new ArrayList<>();
for(Interval i:intervals){
meetings.add(new Meeting(i.start,1));
meetings.add(new Meeting(i.end,-1));
} Collections.sort(meetings,Meeting.comparator); int count =0;
int ans =0;
for(Meeting m:meetings){
if(m.flag==1){
count++;
} if(m.flag==-1){
count--;
} ans = Math.max(ans,count);
} return ans;
}
}
821. Time Intersection
https://www.lintcode.com/problem/time-intersection/description?_from=ladder&&fromId=4
/**
* Definition of Interval:
* public classs Interval {
* int start, end;
* Interval(int start, int end) {
* this.start = start;
* this.end = end;
* }
* }
*/
class Point{
int time;
int flag; Point(int t, int s) {
this.time = t;
this.flag = s;
}
public static Comparator<Point> PointComparator = new Comparator<Point>() {
public int compare(Point p1, Point p2) {
if(p1.time == p2.time)
return p1.flag - p2.flag;
else
return p1.time - p2.time;
}
};
} public class Solution {
/**
* @param seqA: the list of intervals
* @param seqB: the list of intervals
* @return: the time periods
*/
public List<Interval> timeIntersection(List<Interval> seqA, List<Interval> seqB) {
// Write your code here
List<Interval> res = new ArrayList<>();
if(seqA==null || seqB==null){
return res;
} List<Point> list = new ArrayList<>();
for(Interval i:seqA){
list.add(new Point(i.start,1));
list.add(new Point(i.end,-1));
} for(Interval i:seqB){
list.add(new Point(i.start,1));
list.add(new Point(i.end,-1));
} Collections.sort(list,Point.PointComparator); int start =-1;
int count=0;
for(Point p:list){
if(p.flag==1)
count++;
else
count--; if(count==2){
start = p.time;
} if(count==1 && start!=-1){
res.add(new Interval(start,p.time));
start = -1;
}
} return res;
}
}
131. The Skyline Problem
https://www.lintcode.com/problem/the-skyline-problem/description?_from=ladder&&fromId=4
class Pair implements Comparable{
int index; //坐标
int status; //是up还是down
int height; //高度 Pair(int index,int status,int height){
this.index = index;
this.status = status;
this.height = height;
} //先按坐标,再按status,再按高度
public int compareTo(Object o){
Pair p = (Pair)o;
if(this.index==p.index){
if(this.status==p.status){
return this.height - p.height;
}else{
return this.status - p.status;
}
}else{
return this.index- p.index;
}
} }
public class Solution {
/**
* @param buildings: A list of lists of integers
* @return: Find the outline of those buildings
*/
private static int UP = 0;
private static int DOWN = 1;
public List<List<Integer>> buildingOutline(int[][] buildings) {
// write your code here
List<List<Integer>> res = new ArrayList<>();
if(buildings ==null || buildings.length==0||buildings[0].length==0){
return res;
} List<Pair> pairs = new ArrayList<>();
for(int i=0;i< buildings.length;i++){
pairs.add(new Pair(buildings[i][0],UP,buildings[i][2]));
pairs.add(new Pair(buildings[i][1],DOWN,buildings[i][2]));
} Collections.sort(pairs); TreeMap<Integer,Integer> heightMap = new TreeMap<>(); int preIndex =0;
int preHeight =0;
for(Pair pair:pairs){
if(!heightMap.containsKey(pair.height)){
heightMap.put(pair.height,1);
}else{
if(pair.status==UP){
heightMap.put(pair.height,heightMap.get(pair.height)+1);
}else{
heightMap.put(pair.height,heightMap.get(pair.height)-1);
if(heightMap.get(pair.height)==0){
heightMap.remove(pair.height);
}
}
} int currHeight = heightMap.size()==0?0:heightMap.lastKey(); if(preHeight!=currHeight){
if(preHeight!=0 && preIndex!=pair.index){
res.add(eachSkyLine(preIndex,pair.index,preHeight));
} preHeight = currHeight;
preIndex = pair.index;
}
} return res; } private List<Integer> eachSkyLine(int start,int end,int height){
List<Integer> list = new ArrayList<>();
list.add(start);
list.add(end);
list.add(height);
return list;
}
}
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