UVa 10763 - Foreign Exchange

统计国家代号出现的次数，如果去的和来的相等就输出YES即可。

import java.util.*;public class Main10763 {public static void main(String[] args) {Scanner scan = new Scanner(System.in);while(true) {int n = scan.nextInt();if(n == 0) break;int[] a = new int[500000], b = new int[500000];Arrays.fill(a, 0);Arrays.fill(b, 0);int maxg = 0;for(int i=0; i<n; i++) {int mm = scan.nextInt();int nn = scan.nextInt();maxg = max(maxg, max(mm, nn));a[mm] ++;b[nn] ++;}int cnt = 0;for(int i=0; i<=maxg; i++) {if(a[i] != b[i]) {cnt = 1;break;}}if(cnt == 0)System.out.println("YES");elseSystem.out.println("NO");}}public static int max(int a, int b) {if(a >= b)return a;elsereturn b;}}