[Java] 1031. Hello World for U (20)-PAT甲级

1031. Hello World for U (20)
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
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:

Sample Output:
h      !
e      d
l       l

1. n1 == n3
2. n2 >= n1
3. n1为在满足上述条件的情况下的最大值

PS:感谢github用户@fs19910227提供的pull request~