Equalbychar

// This file is a "Hello, world!" in C++ language by GCC for wandbox.
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>

using std::string;
bool equalsChar(string::const_iterator& at1,
                string::const_iterator& at2,
                const char& ch,
                const string::const_iterator& end1,
                const string::const_iterator& end2)
{
    if((at1 == end1) && (at2 == end2))
        return true; // two empty strings are equal, right?
    if(at1 != end1)
    {
       if(at2 != end2)
       {
            if((*at1 != *at2) && (*at1 == ch || *at2 == ch))
                return false;
            return equalsChar( ++at1, ++at2, ch, end1, end2);
       }
       else
       {
            if(*at1 == ch)
                return false;
            return equalsChar( ++at1, at2, ch, end1, end2);
       }
    }
    else {
        if(*at2 == ch ) return false;
        return equalsChar( ++at2, at1, ch,end2, end1);
    }
}

bool equalsChar(const string& strA, const string& strB, char ch)
{
     // maybe do checks if strings are empty to shortcut the function?
     auto it1 = strA.begin(), it2 = strB.begin();
     return equalsChar(it1, it2, ch, strA.end(), strB.end() );
}
/*
bool equalsChar(const string& strA, const string& strB, char ch) {
    if (strA.size() > strB.size()) { return equalsChar(strB, strA, ch); }

    auto common = [ch](char a, char b) { return (a == ch) == (b == ch); };
    return std::equal(strA.begin(), strA.end(), strB.begin(), common)
        && (std::find(strB.begin() + strA.size(), strB.end(), ch) == strB.end());
}*/

int main()
{
    std::vector<std::pair<string,string>> data= {
    { "X", "X" },
    { "aaaXaaaX", "abcXcbaX" },
    { "XaXbXcX", "XtXoXpXdef" },
    { "XaXbXcX", "XtXoXpXdXf" },
    { "XXXX", "XX" },
    { "aXaXbXcX", "XtXoXpX" },
        {"werwerwe","erwer"}};


    for(auto& item : data)
        std::cout << "equalsChar( " << item.first << ", " << item.second  << " )"
              << string{ equalsChar(item.first,item.second,'X') ? " is true" : " is false"} << std::endl;
}