___copy.cpp

#include<cstdio>
#include<iostream>
#include<fstream>
using namespace std;

string exec(const char* cmd){
    string ret;
    char buf[128];

    FILE *f=popen(cmd, "r");
    while(!feof(f))
        if(fgets(buf, 128, f) != NULL)
            ret += buf;
    pclose(f);
    return ret;
}

int main(int argc, char** argv)
{
    string f1=argv[1];//original
    string f2=argv[2];//ncr
    string f3=argv[3];//answer
    string cmd="diff -Z -B --strip-trailing-cr -q "+f2+" "+f3;

    ifstream f1s(f1.c_str()), f2s(f2.c_str());

    if(f1s && f2s)
    {
        string ret=exec(cmd.c_str());
        if(ret.length()==0)//ncr is the same as answer
        {
            cmd="cp "+f3+" "+f1;
            exec(cmd.c_str());
        }
    }
}