S=“S1S2…Sn”是一个长为n的字符串，存放在一个数组中，编程序将S改造之后输出。 S = "S1S2 ... Sn" is a string of length n, and stored in an array, output S after its programmable transformation. 1.将S的所有第偶数个字符按照其原来的下标从大到小的次序放在S的后半部分； 1.All the even-numbered characters of S should be placed in accordance with their subscript descending order in the second half of S; 2.将S的所有第奇数个字符按照其原来的下标从小到大的次序放在S的前半部分； 2.All the odd-numbered characters of S should be placed in accordance with their