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2007年长沙市中考有一道试题如下:在密码学中,直接可以看到内容为明码,对明码进行某种处理后得到的内容为密码.有一种密码,将英文26个字母a,b,c,…,z(不论大小写)依次对应1,2,3,…,26这26个自然数(见表格).当明码对应的序号x为奇数时,密码对应的序号y=(x+1)/2;当明码对应的序号x为偶数时,密码对应的序号y=x/2+13.
Changsha City Examination in 2007 there is a test questions are as follows: In cryptography, you can directly see the contents of the code, the code for some processing obtained after the content of the password. There is a password, the English 26 letters a, b, c , ..., z (regardless of upper and lower case) correspond to 26 natural numbers (see table) corresponding to 1, 2, 3, ..., 26. When the sequence number x corresponding to the plain code is an odd number, the sequence number corresponding to the password y = / 2; when the corresponding code x is an even number, the password corresponding to the serial number y = x / 2 +13.