编程之美-高效地安排会议 图着色问题 贪心算法

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;

public class GraphColoringProblem {

	/**编程之美 高效地安排会议 图着色问题 贪心算法
	 * 假设要用很多个教室对一组活动进行调度。我们希望使用尽可能少的教室来调度所有的活动。请给出一个有效的贪心算法，来确定哪一个活动应使用哪一个教室。
	 * (这个问题也被成为区间图着色(interval-graph coloring)问题。我们可作出一个区间图，其顶点为已知的活动，其边连接着不兼容的活动。
	 * 为使任两个相邻结点的颜色均不相同，所需的最少颜色对应于找出调度给定的所有活动所需的最少教室数。)
	 * see
	 * http://renren.it/a/caozuoxitong/OS/20120626/176363.html
	 */
	public static void main(String[] args) {
		List<Meeting> list=new ArrayList<Meeting>();
		Random random=new Random();
		for(int i=0;i<10;i++){
			int begin=random.nextInt(10)+1;
			int end=begin+(random.nextInt(10)+1);
			Meeting meeting=new Meeting(begin,end);
			list.add(meeting);
		}
		GraphColoringProblem gcp=new GraphColoringProblem();
		gcp.smartManagment(list);
	}

	public void smartManagment(List<Meeting> list){
		if(list==null||list.size()<2){
			return;
		}
		printList(list);
		Collections.sort(list);
		printList(list);
		List<List<Meeting>> outerList=new ArrayList<List<Meeting>>();
		while(list.size()!=0){
			int size=list.size();
			List<Meeting> listOfOneRoom=new ArrayList<Meeting>();
			Meeting current=list.get(0);
			listOfOneRoom.add(current);
			for(int i=1;i<size;i++){
				Meeting candidate=list.get(i);
				if(candidate.begin>=current.end){
					listOfOneRoom.add(candidate);
					current=candidate;
				}
			}
			outerList.add(listOfOneRoom);
			list.removeAll(listOfOneRoom);
		}
		//meetings that can be held in the same room are printed in one line:
		for(int i=0,size=outerList.size();i<size;i++){
			printList(outerList.get(i));
		}
	}
	
	static class Meeting implements Comparable<Meeting>{
		int begin;
		int end;
		Meeting(int begin,int end){
			this.begin=begin;
			this.end=end;
		}
		public int compareTo(Meeting o) {
			int endCmp=this.end-o.end;
			if(endCmp==0){
				return this.begin-o.begin;
			}
			return endCmp;
		}
		public String toString(){
			return "["+begin+","+end+"]";
		}
	}
	
	public static void printList(List<Meeting> list){
		if(list==null||list.size()==0){
			return;
		}
		for(int i=0,size=list.size();i<size;i++){
			System.out.print(list.get(i));
		}
		System.out.println();
	}
}