2014 Liaoning Province game Traveling

Question K: Traveling

Time Limit: 1 Sec memory limit: 128 MB
Submission: 13 solution: 4
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Description

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.

Input

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.

Output

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

Sample Input

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

Sample output

NO YES

Prompt

This question is not difficult, and the data scope is not big. You only need to simulate the process. For details, see the code.

#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"<