说明：  回文字符串是指从左到右和从右到左相同的字符串。 现给定一个仅由小写字母组成的字符串，你可以把它的字母重新排列，以形成不同的回文字符串。 * 输入：非空仅由小写字母组成的字符串，长度不超过100； 输出：能组成的所有回文串的个数（因为结果可能非常大，输出对1000000007取余数的结果）。 * 例如：输入"aabb" 输出为2（因为“aabb”对应的所有回文字符串有2个：abba和baab）
(Palindrome string is from left to right and right to left the same string. Now only given a string of lowercase letters, you can put it to rearrange the letters to form different palindrome string.* Input: only by a non-empty string consisting of lowercase letters, the length does not exceed 100 Output: palindrome string can be composed of all the number (because the result can be very large, the output on 1000000007 to take the remainder of the results).* For example: Enter " aabb" output is 2 (because " aabb" all corresponding palindrome string has two: abba and baab))