PAT 1002 Hello World for U (20)

Given any string of N (>=5) characters, you are asked to form the characters into the shape of U. For example, "helloworld"
can be printed as:

h  d
e  l
l  r
lowo

That is, the characters must be printed in the original order, starting top-down from the left vertical line with n1 characters,
then left to right along the bottom line with n2 characters, and finally bottom-up along the vertical line with n3 characters. And more, we would like U to be as squared as possible -- that is, it must be satisfied that n1 = n3 = max { k| k <= n2 for all 3
<= n2 <= N } with n1 + n2 + n3 - 2 = N. 

输入描述:

Each input file contains one test case.  Each case contains one string with no less than 5 and no more than 80 characters in a line.  The string contains no white space.

输出描述:

For each test case, print the input string in the shape of U as specified in the description.

输入例子:

helloworld!

输出例子:

h   !
e   d
l   l
lowor

#include <iostream>
#include <cstring>
#include <string>

using namespace std;

int main()
{
int i1,i2,left_right,down,i,j,k;
char s[1024];
while(cin>>s)
{

i1=(strlen(s)+2)/3;
i2=(strlen(s)+2)%3;
if(1==i2)
{
left_right=i1;
down=i1+1;
}
else if(2==i2)
{
left_right=i1;
down=i1+2;
}
else
{
left_right=down=i1;
}
for(i=0,k=0;i<left_right-1;i++)
{
cout<<s[k];
for(j=2;j<down;j++)
cout<<" ";
cout<<s[strlen(s)-1-k]<<endl;
k++;
}
for(i=k;i<strlen(s)-k;i++)
cout<<s[i];
cout<<endl;
}
return 0;
}

插个图