misc. c plus plus exercises

shifts.cc

#include <iostream>
#include <string>

#define swap(a, b) { \
    a ^= b; \
    b ^= a; \
    a ^= b;}

std::string& reverse(std::string& str, int start, int end) {
    if (end == start) return str;
    int i = start, j = end;
    while (i < j) {
        swap(str[i], str[j]);
        ++i;
        --j;
    }
    return str;
}

std::string& shift_n(std::string& str, int n) {
    int len = str.length();
    n = n % len;
    reverse(str, 0, n-1);
    reverse(str, n, len-1);
    return reverse(str, 0, len-1);
}

std::string& _shift(std::string& str, int s, int n) {
    // std::cout<<"[debug1:] "<<str<<std::endl;
    int len = str.length() - s;
    n = n % len;
    // std::cout<<"[debug2:] "<<s<<" "<<n<<" "<<len<<std::endl;    
    if (n == 0) return str;
    int i = s;
    while(i < s + n && i < s + len - n) {
        swap(str[i], str[n+i]);
        i++;
    }
    if (n+n >= len) {
        n = n+n-len;
    }
    return _shift(str, i, n);
}

std::string& shift_m(std::string& str, int m) {
    return _shift(str, 0, m);
}

std::string& operator<<(std::string& str, int n) {
    return _shift(str, 0, n);
}

std::string& operator>>(std::string& str, int n) {
    return _shift(str, 0, str.size()-n);
}

int main(int argc, char const *argv[])
{
    int n;
    if (argc < 2) n = 5;
    else n = atoi(argv[1]);
    std::string in("abcdefg");
    std::cout<<in<<std::endl;
    // shift_n(in, 13);
    // std::cout<<in<<std::endl;
    shift_m(in, n);
    std::cout<<in<<std::endl;
    std::cout<<(in<<4)<<std::endl<<(in>>2)<<std::endl;
    return 0;
}