PAT 1031. Hello World for U (20)

http://pat.zju.edu.cn/contests/pat-a-practise/1031

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 n1characters,
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.

Input Specification:

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.

Output Specification:

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

helloworld!

Sample Output:

h   !
e   d
l   l
lowor

#include <cstdio>
#include <cstring>

int main(){
char s[81];
scanf("%s", s);
int n = strlen(s);
int a, b;
int max = -1;
for (int j = 3; j <= n; ++j){
for (int i = 1; i <= j; ++i){
if (2 * i + j == n + 2){
if (i > max)
max = i;
}
}
}
a = max;
b = n + 2 - 2 * a;
for (int i = 0; i < a - 1; i++){
printf("%c", s[i]);
for (int k = 0; k < b - 2; k++)
printf(" ");
printf("%c\n", s[n - i -1]);
}
for (int l = a - 1; l < b + a- 1; l++)
printf("%c", s[l]);
printf("\n");
return 0;
}