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/*
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* C++ Program to Decode a Message Encoded Using Playfair Cipher
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This C++ program decodes any message encoded using the technique of traditional playfair cipher. The Playfair cipher or Playfair square is a manual symmetric encryption technique and was the first literal digraph substitution cipher. Input is not case sensitive and works only for characters from ‘a’ to ‘z’ and ‘A’ to ‘Z’.
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*/
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#include<iostream>
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#include<vector>
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using namespace std;
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const char encoder[5][5] = {{'A','B','C','D','E'},
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{'F','G','H','I','K'},
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{'L','M','N','O','P'},
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{'Q','R','S','T','U'},
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{'V','W','X','Y','Z'}
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};
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void input_string(vector<char>& a)
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{
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char c;
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while (1)
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{
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c=getchar();
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if (c >= 97 && c <= 122)
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c -= 32;
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if (c == '\n')
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break;
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else if (c==' ')
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continue;
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else if (c == 'J')
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a.push_back('I');
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a.push_back(c);
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}
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return;
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}
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void get_pos(char p, int& r, int& c)
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{
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if (p < 'J')
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{
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r = (p - 65) / 5;
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c = (p - 65) % 5;
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}
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else if (p > 'J')
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{
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r = (p - 66) / 5;
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c = (p - 66) % 5;
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}
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return;
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}
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void same_row(int r, vector<char>& code, int c1, int c2)
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{
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code.push_back(encoder[r][(c1 + 4) % 5]);
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code.push_back(encoder[r][(c2 + 4) % 5]);
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return;
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}
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void same_column(int c, vector<char>& code, int r1, int r2)
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{
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code.push_back(encoder[(r1 + 4) % 5][c]);
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code.push_back(encoder[(r2 + 4) % 5][c]);
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return;
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}
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void diff_col_row(int r1, int c1, vector<char>& code, int r2, int c2)
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{
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code.push_back(encoder[r1][c2]);
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code.push_back(encoder[r2][c1]);
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return;
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}
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void encode(vector<char> msgx, int len)
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{
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vector<char> code;
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int i = 0, j = 0;
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int r1, c1, r2, c2;
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while (i < len)
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{
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get_pos(msgx[i], r1, c1);
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i++;
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get_pos(msgx[i], r2, c2);
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if (r1 == r2)
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{
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same_row(r1, code, c1, c2);
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}
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else if (c1 == c2)
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{
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same_column(c1, code, r1, r2);
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}
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else
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{
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diff_col_row(r1, c1, code, r2, c2);
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}
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i++;
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}
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cout<<"\nCODE: ";
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for (j = 0; j < code.size(); j++)
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{
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if (code[j] == 'X')
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continue;
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cout<<code[j];
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}
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return;
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}
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int main()
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{
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vector<char> msg;
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std::cout<<"Enter the Encrypted Message:";
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input_string(msg);
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int len=msg.size();
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encode(msg,len);
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return 0;
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}
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/*
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Enter the Encrypted Message:CBNVMPPO
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CODE: BALLOON
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