Language used : C++
include
using namespace std;
int top =1,top2;
int push(int arr3[],int x, int size)
{
top++;
arr3[top] = x;
}
int pop()
{
top = top - 1;
}
int topi(){
return top;
}
bool isempty(){
if (top == -1)
return false;
else
return true;
}
int main()
{
int a,b,c,d,e,f,g,h,i,m;
while(1)
{
scanf("%d",&a);
if(a==0)
break;
else
{
int arr[a+1],arr2[a+1],arr3[a+1];
for(b=0;b<a;b++)
{
scanf("%d",&arr[b]);
arr2[b] = arr[b];
}
sort(arr,arr+a);//arr sorted arr2 original 1 2 2 1 a=2;
i=0;
int l=0;
arr3[topi()] = 0;
for(c=0;c<a;c++)
{
for(b=l;b<a;b++)
{
if (arr[c] == arr3[topi()])
{
pop();
i++;b = b-1;
break;
}
else if(arr[c] != arr2[b])
{push(arr3,arr2[b],a);
}
else if (arr[c] == arr2[b])
{
i++;
break;
}
}
l = b+1;
if(l == a)
break;
else
{m++;}
}
for(e=0;e<a;e++)
{
if(arr[e] == arr3[topi()])
{
i++;
pop();
}
}
}
if(i == a)
printf("yes\n");
else
printf("no\n");
}}