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 n ₁ characters, then left to right along the bottom line with n ₂  characters, and finally bottom-up along the vertical line with n ₃  characters. And more, we would like U to be as squared as possible -- that is, it must be satisfied that n ₁  = n ₃  = max { k| k <= n ₂  for all 3 <= n ₂  <= N } with n ₁  + n ₂  + n ₃  - 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;
}