题目地址
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<iostream>
#include<string.h>
using namespace std;
int main(){
    string s;
    cin>>s;
    int n=s.length(),n1=(n+2)/3;        //核心就是这个公式，还有as squared as possible
    int n3=n1,n2=n-n1-n3+2;
    for(int i=0;i<n1-1;i++){
        cout<<s[i];
        for(int j=0;j<n2-2;j++) cout<<" ";
        cout<<s[n-i-1]<<endl;
    }
    for(int i=n1-1;i<n1-1+n2;i++) cout<<s[i];
}