这题陷阱真多，贴一下 JAVA 的解答， 供后来者参考。 
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;

public class Main {

	/**
	 * @param args
	 * @throws IOException 
	 */
	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub
		int N = 0; 
		int T = 0; 
		BufferedReader br 
		   = new BufferedReader(new InputStreamReader(System.in));
		String str = br.readLine();
		StringTokenizer stoken = new StringTokenizer(str," ");
		N = Integer.valueOf(stoken.nextToken());
		T = Integer.valueOf(stoken.nextToken());
		
		List<Shift> list = new ArrayList<Shift>();
		for (int i = 0; i < N; i++) {
			str = br.readLine();
			stoken= new StringTokenizer(str, " ");
			list.add(new Shift(
					Integer.valueOf(stoken.nextToken()),
					Integer.valueOf(stoken.nextToken())
					));
		}
		
		Collections.sort(list,new MyComparator());
//		System.out.println(list);

		int count= 0 ; 
		if( list.get(0).begin != 1 	)
		{
			System.out.println("-1");
			return ;
		}
		int tmp = list.get(0).end;
		
		if( list.size() == 1 && tmp < T ) 
		{
			System.out.println("-1");
			return ;
		}
		
		if( tmp >= T ) 
		{
			System.out.println("1");
			return ;
		}
		
		count ++;
		
		int i = 1;
		int max = 0;
		while( i < list.size() )
		{
			boolean flag = false; 
			max = list.get(i).begin;
			while( i < list.size() && list.get(i).begin <= tmp + 1 )
			{
				flag = true;
				if( max< list.get(i).end ) max = list.get(i).end;
				i++;
			}
			
//			System.out.println("max = " + max );
			if( flag == false ) 
			{
				System.out.println("-1");
				return ;
			}
			count++;
			if( max >= T ) 
			{
				System.out.println(count);
				return ;
			}
			tmp = max;
		}
		if( max < T ) System.out.println("-1");
		else System.out.println(count);
		br.close();
	}
}

class Shift 
{
	int begin = 0; 
	int end = 0; 
	int du = 0;
	public Shift( int in_begin , int in_end )
	{
		begin = in_begin; 
		end = in_end;
		du = getDu();
	}
	
	public String toString() 
	{
	  return "(" + begin + "," + end + "," + du + ")";
	}
	
	public int getDu()
	{
		return end - begin;
	}
}

class MyComparator implements Comparator<Shift>
{
	public int  compare(Shift a , Shift b )
	{
		if( a.begin > b.begin ) return 1; 
		else if( a.begin == b.begin ) 
		{
			if( a.end > b.end ) return -1; 
			else if( a.end == b.end ) return 0; 
			else return 1;
		}
		else  return -1;
	}
}