分析

首先，飞机飞过去，消耗的时间是(从china往usa加一个时差)   end-start+time
然后，飞机从usa飞到china，然后减一个时差    end-start-time
两式合并    end1-start1+end2—start2=2*t
            t=(end1-start1+end2—start2)/2
ps:java版由于没那个sscanf，只能截取字符串，很恶心

java 代码

 public class Main {
    static BufferedReader buf=new BufferedReader(new InputStreamReader(System.in));
    private static int get_second(int h,int m,int s)
    {
        return 3600*h+m*60+s;
    }
    private static int get_time() throws IOException
    {
        String str=buf.readLine();
        int day=0;
        if(str.charAt(str.length()-1)==')')
        {
            day=Integer.parseInt(""+str.charAt(str.length()-2));
            str=str.substring(0, str.length()-5);
        }
        String s[]=str.split(" ");
        String s1[]=s[0].split(":");
        String s2[]=s[1].split(":");
        int a1=Integer.parseInt(s1[0]);
        int a2=Integer.parseInt(s1[1]);
        int a3=Integer.parseInt(s1[2]);
        int b1=Integer.parseInt(s2[0]);
        int b2=Integer.parseInt(s2[1]);
        int b3=Integer.parseInt(s2[2]);
        return  get_second(b1, b2, b3)-get_second(a1, a2, a3)+day*24*3600;
    }
    public static void main(String args[]) throws IOException
    {
        int n=Integer.parseInt(buf.readLine());
        while(n--!=0)
        {
            int time=(get_time()+get_time())/2;
            int hour=time/3600;
            int minute=time%3600/60;
            int secound=time%60;
            System.out.printf("%02d:%02d:%02d", hour,minute,secound);
            System.out.println();
        }
    }
}