Create a new string with duplicates of each character in the original string and append the reverse of the same string (with duplicates) excluding the last character

Question

Given a string say "ABCD". Now create a new string with duplicates of each character in the original string and append the reverse of the same string (with duplicates) excluding the last character.

First iteration: AABBCCCCBBAA

[ABC three types of chars; Here c is the last char.Ignore duplicates after the last char c]

Second iteration: AABBBBAA

[here b is the last char]

Third iteration: AAAA

[no second char left]

Solution

#include <iostream>

#include <iomanip>

#include <string>

#include <cassert>

using namespace std;

string CreateString(const string& str)

{

assert(str.length() > 0);

string ret(str.length() * 4 - 4, ' ');

int index(0);

for (int i = 0; i < str.length() - 1; ++i)

{

ret.at(index++) = str.at(i);

ret.at(index++) = str.at(i);

}

for (int i = str.length() - 2; i >= 0; --i)

{

ret.at(index++) = str.at(i);

ret.at(index++) = str.at(i);

}

return ret;

}

int main()

{

cout << CreateString(string("a")) << endl;

cout << CreateString(string("ab")) << endl;

cout << CreateString(string("abcd")) << endl;

cout << CreateString(string("abcdefg")) << endl;

return 0;

}

Output

aaaa

aabbccccbbaa

aabbccddeeffffeeddccbbaa

Press any key to continue . . .