2014辽宁省赛 Traveling

问题 K: Traveling

时间限制: 1 Sec 内存限制: 128 MB
提交: 13 解决: 4
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题目描述

SH likes traveling around the world. When he arrives at a city, he will ask the staff about the number of cities that connected with this city directly. After traveling around a mainland, SH will collate data and judge whether the data is correct.

A group of data is correct when it can constitute an undirected graph.

输入

There are multiple test cases. The first line of each test case is a positive integer N (1<=N<=10000) standing for the number of cities in a mainland. The second line has N positive integers a1, a2, ...,an. ai stands for the number of cities that connected directly with the ith city. Input will be ended by the END OF FILE.

输出

If a group of data is correct, output "YES" in one line, otherwise, output "NO".

样例输入

8 7 7 4 3 3 3 2 1 10 5 4 3 3 2 2 2 1 1 1

样例输出

NO YES

提示

这道题不难，数据范围也不大，只需要进行过程的模拟，详见代码

#include
  
   
#include
   
     #include
    
      #include
     
       #include
      
        using namespace std; const int MAX=10005; int f[MAX]; int main() { int n; while(scanf("%d",&n)!=EOF) { for(int i=0;i
       
        0&&p
        
         0) { f[p-1]--; f[i]--; } } if(f[i]!=0) { cout<<"NO"<