Traveling

Traveling

时间限制: 1 Sec  内存限制: 128 MB
提交: 15  解决: 5
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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

87 7 4 3 3 3 2 1105 4 3 3 2 2 2 1 1 1

样例输出

NOYES

提示

来源

辽宁省赛2014

#include<iostream>using namespace std;int a[10010];int main(){    int n;    while(cin>>n){        int i,j;        for(i=0;i<n;i++)            cin>>a[i];        for(i=0;i<n;i++){            for(j=i+1;j<n;j++){                if(a[i]>0 && a[j]>0){                    a[i]--;                    a[j]--;                }            }            if(a[i]!=0){                cout<<"NO"<<endl;                break;            }        }        if(i>=n)            cout<<"YES"<<endl;    }    return 0;}