【模拟】[NOIP2012]Vigenère密码

最新推荐文章于 2024-08-01 12:03:26 发布

jiangzh7

最新推荐文章于 2024-08-01 12:03:26 发布

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本文介绍了NOIP2012竞赛中涉及的Vigenère密码，强调在处理该密码时应注意避免手动创建完整的字母表表格，而应使用0到25的数字表示并加上'A'进行转换。同时还提供了C++代码实现。

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Vigenère密码

(vigenere.cpp/c/pas)

【问题描述】
16 世纪法国外交家Blaise de Vigenère设计了一种多表密码加密算法——Vigenère密码。Vigenère 密码的加密解密算法简单易用，且破译难度比较高，曾在美国南北战争中为
南军所广泛使用。
在密码学中，我们称需要加密的信息为明文，用 M 表示；称加密后的信息为密文，用C 表示；而密钥是一种参数，是将明文转换为密文或将密文转换为明文的算法中输入的数据，记为k。在Vigenère密码中，密钥k是一个字母串， k=k1k2…kn。当明文M=m1m2…mn时，得到的密文C=c1c2…cn，其中ci=mi®ki，运算®的规则如下表所示：

Vigenère加密在操作时需要注意：
1. ®运算忽略参与运算的字母的大小写，并保持字母在明文 M中的大小写形式；
2. 当明文M的长度大于密钥k的长度时，将密钥k 重复使用。
例如，明文M=Helloworld，密钥k=abc 时，密文C=Hfnlpyosnd。
明文 H e l l o w o r l d
密钥 a b c a b c a b c a
密文 H f n l p y o s n d

【输入】
输入文件名为vigenere.in。
输入共2行。
第一行为一个字符串，表示密钥k，长度不超过100，其中仅包含大小写字母。第二行
为一个字符串，表示经加密后的密文，长度不超过1000，其中仅包含大小写字母。

【输出】
输出文件名为vigenere.out。
输出共1行，一个字符串，表示输入密钥和密文所对应的明文。

【输入输出样例】

vigenere.in	vigenere.out
CompleteVictory Yvqgpxaimmklongnzfwpvxmniytm	Wherethereisawillthereisaway

【数据说明】
对于 100%的数据，输入的密钥的长度不超过 100，输入的密文的长度不超过 1000，且都仅包含英文字母。

题目不难，只是打表要注意方式，不要去打'A','B','C'...，那样会打很久，直接打0..25即可，每次用的时候加上'A'（pascal加上ord('A')），再进行其他操作

C++ Code

/*
C++ Code
http://blog.youkuaiyun.com/jiangzh7
By Jiangzh
*/
#include<cstdio>
#include<cstring>
#include<string>
#include<cmath>
#include<cctype>
#include<iostream>
#include<algorithm>
using namespace std;

const int kkk[26][26]={
    {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25},
    {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,0},
    {2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,0,1},
    {3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,0,1,2},
    {4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,0,1,2,3},
    {5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,0,1,2,3,4},
    {6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,0,1,2,3,4,5},
    {7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,0,1,2,3,4,5,6},
    {8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,0,1,2,3,4,5,6,7},
    {9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,0,1,2,3,4,5,6,7,8},
    {10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,0,1,2,3,4,5,6,7,8,9},
    {11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,0,1,2,3,4,5,6,7,8,9,10},
    {12,13,14,15,16,17,18,19,20,21,22,23,24,25,0,1,2,3,4,5,6,7,8,9,10,11},
    {13,14,15,16,17,18,19,20,21,22,23,24,25,0,1,2,3,4,5,6,7,8,9,10,11,12},
    {14,15,16,17,18,19,20,21,22,23,24,25,0,1,2,3,4,5,6,7,8,9,10,11,12,13},
    {15,16,17,18,19,20,21,22,23,24,25,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14},
    {16,17,18,19,20,21,22,23,24,25,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15},
    {17,18,19,20,21,22,23,24,25,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16},
    {18,19,20,21,22,23,24,25,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17},
    {19,20,21,22,23,24,25,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18},
    {20,21,22,23,24,25,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19},
    {21,22,23,24,25,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20},
    {22,23,24,25,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21},
    {23,24,25,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22},
    {24,25,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23},
    {25,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24}
};

string s,mi;

void init()
{
    freopen("vigenere.in","r",stdin);
    freopen("vigenere.out","w",stdout);
    
    string temp;
    cin>>s;temp=s;
    cin>>mi;
    while(s.length()<mi.length()) s+=temp;
    //cout<<s<<endl<<mi<<endl;
}

char find(char x,char y)
{
    bool sign=false;
    if(y>='A' && y<='Z') sign=true;
    x=tolower(x);y=tolower(y);
    char ans;
    for(int i=0;i<26;i++)
        if(kkk[x-'a'][i]==y-'a') {ans=i+'a';break;}
    if(sign) ans=toupper(ans);
    return ans;
}

void work()
{
    for(int i=0;i<mi.length();i++)
        cout<<find(s[i],mi[i]);
}

int main()
{
    init();
    work();
    return 0;
}