Equivalent Strings（二分+递归深搜）

Link：http://codeforces.com/contest/559/problem/B

B. Equivalent Strings

time limit per test
2 seconds

memory limit per test
256 megabytes

input
standard input

output
standard output

Today on a lecture about strings Gerald learned a new definition of string equivalency. Two strings a and b of
equal length are calledequivalent in one of the two cases:

They are equal.

If we split string a into two halves of the same size a1 and a2,
and string b into two halves of the same size b1 and b2,
then one of the following is correct:

a1 is
equivalent to b1,
and a2 is
equivalent to b2

a1 is
equivalent to b2,
and a2 is
equivalent to b1

As a home task, the teacher gave two strings to his students and asked to determine if they are equivalent.

Gerald has already completed this home task. Now it's your turn!

Input

The first two lines of the input contain two strings given by the teacher. Each of them has the length from 1 to 200 000 and
consists of lowercase English letters. The strings have the same length.

Output

Print "YES" (without the quotes), if these two strings are equivalent, and "NO"
(without the quotes) otherwise.

Sample test(s)

input

aaba
abaa

output

YES

input

aabb
abab

output

NO

Note

In the first sample you should split the first string into strings "aa" and "ba",
the second one — into strings "ab" and "aa". "aa"
is equivalent to "aa"; "ab" is equivalent to "ba"
as "ab" = "a" + "b",
"ba" = "b" + "a".

In the second sample the first string can be splitted into strings "aa" and "bb",
that are equivalent only to themselves. That's why string "aabb" is equivalent only to itself and to string "bbaa".

AC code：

#include<iostream>
#include<cstring>
#include<cstdio>
#include<cmath>
using namespace std;
string s1,s2;
string equ(string s)
{
	int lens=s.length();
	if(lens&1)
		return s;
	string s1=equ(s.substr(0,lens/2));
	string s2=equ(s.substr(lens/2,lens/2));
	if(s1<s2)
		return s1+s2;
	else
		return s2+s1;
}
int main()
{
	while(cin>>s1>>s2)
	{
		if(equ(s1)==equ(s2))
			printf("YES\n");
		else
			printf("NO\n");
	}
	return 0;
}