Misc

【真签到题】快来看直播啦~

打开直播间，即可在直播画面内找到flag

因此flag为 HECTF{狮虎萌轻一点打出题人好吗嘤嘤嘤}

Author: JiJi, XiaoZhuo, Accelerat0r. All rights reserved.

Reverse

Welcome To Re!

下载得到一个 Signin.zip 的压缩包，解压后找到ELF文件，用ida64反编译后得到

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int __cdecl main(int argc, const char **argv, const char **envp)
{
  char s2[8]; // [rsp+0h] [rbp-70h]
  char s1; // [rsp+30h] [rbp-40h]
  unsigned __int64 v6; // [rsp+68h] [rbp-8h]
  v6 = __readfsqword(0x28u);
  strcpy(s2, "moectf{W3lc0me-T0_th3-W0rld_Of_R3v3rsE!}");
  puts("Welcome to MoeCTF! --by Reverier\nPlease Input your flag and I will check it:");
  __isoc99_scanf("%41s", &s1);
  if ( !strcmp(&s1, s2) )
    puts("Congratulations!");
  else
    puts("Ruaaaaaaaaaaaaa~~~Wrong!");
  return 0;
}

因此flag为 moectf{W3lc0me-T0_th3-W0rld_Of_R3v3rsE!}

Nezzar and Lucky Number

Nezzar's favorite digit among $1,…,9$ is $d$. He calls a positive integer lucky if $d$ occurs at least once in its decimal representation.

Nezzar and Colorful Balls

Nezzar has $n$ balls, numbered with integers $1,2,…,n$. Numbers $a_1,a_2,…,a_n$ are written on them, respectively. Numbers on those balls form a non-decreasing sequence, which means that $a_i≤a_{i+1}$ for all $1≤i<n$.

New Year's Number

Polycarp remembered the $2020$-th year, and he is happy with the arrival of the new $2021$-th year. To remember such a wonderful moment, Polycarp wants to represent the number $n$ as the sum of a certain number of $2020$ and a certain number of $2021$.

Odd Divisor

You are given an integer $n$. Check if $n$ has an odd divisor, greater than one (does there exist such a number $x$ ($x>1$) that $n$ is divisible by $x$ and $x$ is odd).

拯救007

在老电影“007之生死关头”(Live and Let Die)中有一个情节，007被毒贩抓到一个鳄鱼池中心的小岛上，他用了一种极为大胆的方法逃脱 —— 直接踩着池子里一系列鳄鱼的大脑袋跳上岸去！(据说当年替身演员被最后一条鳄鱼咬住了脚，幸好穿的是特别加厚的靴子才逃过一劫。)

Wizard of Orz

There are $n$ digital panels placed in a straight line. Each panel can show any digit from $0$ to $9$. Initially, all panels show $0$.

扫描集

扫描集为一个字符集合，用来匹配期待输入的字符。对于scanf匹配输入内容时，可以使用扫描集灵活地进行字符串截取输入。

扫描集以 % 开头，用 [] 包含字符集。如扫描集 %[abc], %[a-z], %[^abc], %[^a-z] ，其中 ^ 表示求反集。

在阅读文章前，请先思考下面的代码执行结果是什么：

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#include <stdio.h>
int main(){
  struct{
    int x; int y;
  }s[2] = {{2, 0}, {1, 3}}, *p = s;
  printf("%d, %d", ++p->x, (++p)->x);
  return 0;
}