CCF201809-2:买菜(JAVA版)

import java.util.Scanner;

public class Main{
    static int N = 1000010;
    static int cnt[] = new int[N];
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int res = 0;
        for(int i = 1; i <= n*2 ; i++) {
            int a = scanner.nextInt();
            int b = scanner.nextInt();
            for(int j = a; j < b ; j ++) {
                cnt[j]++;
                if(cnt[j]==2) res++;
            }
        }
        System.out.println(res);
    }
}