题解 | #字符串加密#

using System;

class Program {
    public static void Main() {
        // 1 Build mapping.
        var table = new char[256];
        var used = new bool['z'-'a'+1];
        var offset = 0;
        for (var c=Console.Read(); c!='\n'; c=Console.Read()) {
            if (!used[c-'a']) {
                table['a'+offset] = (char)c;
                table['A'+offset] = char.ToUpper((char)c);
                ++offset;
                used[c-'a'] = true;
            }
        }
        for(var i=0; i<used.Length; ++i) {
            if (!used[i]) {
                table['A'+offset] = (char)('A'+i);
                table['a'+offset] = (char)('a'+i);
                ++offset;
            }
        }
        // 2 Encrypt.
        for (var c=Console.Read(); c!='\n'; c=Console.Read()) {
            Console.Write(table[c]);
        }
    }
}