【PAT Advanced Level】1031. Hello World for U (20)

#include <iostream>
#include <string>
using namespace std;

int main()
{
string s;
cin>>s;
int n1, n2;
n2 = (s.size() % 2 == 1)?3 : 4;
while (n2 <= s.size())
{
n1 = (s.size() - n2)/2 + 1;
if(n1 <= n2) break;
n2 += 2;
}
int i = 0;
for(; i < n1 - 1; i++)
{
cout<<s[i];
for(int j = 0; j < n2 - 2; j++)
cout<<" ";
cout<<s[s.size() - i - 1]<<endl;
}
for(int j = i; j < s.size() - i; j++)
cout<<s[j];
cout<<endl;
}