题解 | #扭蛋机#

using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;
public class Program {
    public static void Main() {
        string line;
        while ((line = System.Console.ReadLine ()) != null) { // 注意 while 处理多个 case
            int n = int.Parse(line);
            StringBuilder sb = new StringBuilder();
            //倒推，扭蛋顺序存入sb
            while(n != 0){
                if(n % 2 == 0){
                    sb.Append("3");
                    n = (n - 2) / 2;
                }
                else{
                    sb.Append("2");
                    n = (n - 1) / 2;
                }
            }
            //反转sb
            StringBuilder result = new StringBuilder(sb.Length);
            for(int i = sb.Length - 1; i >= 0; i--){
                result.Append(sb[i]);
            }
            Console.WriteLine(result.ToString());
        }
    }
}

从n反推扭蛋顺序，n为偶数则最后一次必是3号扭蛋机，奇数则是2号，一直反推到n=0；