题解：

https://www.luogu.org/problemnew/solution/P2123

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.StreamTokenizer;
import java.util.Arrays;
import java.util.Comparator;

public class Main {

	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub
		System.setProperty("java.util.Arrays.useLegacyMergeSort", "true");
		PrintWriter out=new PrintWriter(new OutputStreamWriter(System.out));
		StreamTokenizer in=new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
		in.nextToken();
//		Scanner sc=new Scanner(System.in);
		int t=(int)in.nval;
//		in.nextToken();
		while(t-->0) {
			in.nextToken();
			int n=(int)in.nval;
//			in.nextToken();
			long sum=0;
			Ad[] admin=new Ad[n];
			for(int i=0;i<n;i++) {
				in.nextToken();
				admin[i]=new Ad();
				admin[i].l=(int)in.nval;
				in.nextToken();
				admin[i].r=(int)in.nval;
				if(admin[i].l>admin[i].r)
					admin[i].d=1;
				else if(admin[i].l<admin[i].r)
					admin[i].d=-1;
				else
					admin[i].d=0;
			}
			Comparator<Ad> cmp=new Comparator<Ad>() {
				
				@Override
				public int compare(Ad o1, Ad o2) {
					// TODO Auto-generated method stub
					if(o1.d!=o2.d)
						return o2.d-o1.d;
					if(o1.d<=0) return o2.l-o1.l;
					return o1.r-o2.r;
				}
			};
			Arrays.sort(admin,cmp);
			sum=admin[n-1].l;
			long c=admin[n-1].l+admin[n-1].r;
			for(int i=n-2;i>=0;i--) {
				sum+=admin[i].l;
				c=Math.max(c, sum)+admin[i].r;
			}
			out.println(c);
		}
		
		out.flush();
		out.close();
	}


}
class Ad{
	int l;
	int r;
	int d;
}