WA 为什么错？请dl解释

https://vjudge.net/contest/336391#problem/C

#include<iostream>
using namespace std;
int stack[1023],a[1004],top=0,k=0,n;// 第k辆车 
int main()
{
    while(cin>>n&&n>0)
    {
        while(cin>>a[1]&&a[1])
        {
            k=0;top=0; 
            for(int i=2;i<=n;i++)cin>>a[i];
            for(int i=1;i<=n;i++)//N2 
            {
                while(a[i]!=stack[top])//N1 
                {
                    stack[++top]=++k;   
                    if(k>n)
                    {
                        cout<<"NO"<<endl;
                        k=-1;break;//N1 
                    }
                }
                if(k==-1)break;//N2 
                top--;
            }
            if(k!=-1)cout<<"YES"<<endl; 
        }
        cout<<endl;
    }   
 }