PAT甲级——A1031 Hello World for U

Given any string of N (≥) 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 } 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 <iostream>
#include <string>
using namespace std;
int main()
{
    string str, s;
    cin >> str;
    int m = (str.length() + 2) / 3;
    s.assign(str.length() - 2 * m, ' ');
    for(int i=0;i<m-1;++i)
        cout << str[i] << s << str[str.length() - i - 1] << endl;
    s.assign(str.begin() + m - 1, str.end() - m + 1);
    cout << s << endl;
    return 0;    
}