1031 Hello World for U

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.

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

deduction ： 

n1 + n2 + n3 = N + 2;

n1 = n3;

Middle space = n2 - 2;

2*n1 + n2 = N + 2;

n1 ​= n3 ​= max { k | k ≤ n2​ for all 3 ≤ n2​ ≤ N } namely n1、n3<=n2;

n2 = N - 2*n1 + 2 >= n1;

N + 2 >= 3*n1;

n1 <= (N+2)/3;

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

int main() {
	string s;
	cin >> s;
	int N = s.size();
	int n1 = (N + 2) / 3;
	int n2 = N + 2 - 2 * n1;
	for (int i = 0; i <= n1 - 2; i++) {
		cout << s[i];
		for (int j = 1; j <= n2 - 2; j++) {
			cout << ' ';
		}
		cout << s[N - i - 1];
		cout << endl;
	}
	for (int i = n1 - 1; i <= n1 - 1 + n2 - 1; i++) {
		cout << s[i];
	}
	return 0;
}