HECTF 2020 Writeup

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}

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MoeCTF 2020 Writeup

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!}

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Codeforces Round 698 B 题解

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.

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Codeforces Round 698 A 题解

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 $1≤i<n$.

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Codeforces Round 697 B 题解

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 $2021$.

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Codeforces Round 697 A 题解

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).

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PTA 拯救007 题解

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。)

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scanf的高级用法

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。

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