arbitrary_pos.cpp

// convert integer to an arbitrary position system
// enumerate/generate password dictionary in lexicographic order

#include <iostream>
#include <string.h>
#include <algorithm>
using namespace std;

char* conv(int x, char* dict, char* buf, int alpha=0) {
    int i = 0;
    int n = strlen(dict);
    if (alpha) x++;
    do {
        if (alpha) x--;
        buf[i++] = dict[x % n];
        x /= n;
    } while (x);
    buf[i] = 0;
    reverse(buf, buf+i);
    return buf;
}

int rconv(char * buf, char * dict, int alpha=0) {
    int i = 0;
    int n = strlen(dict);
    int k = strlen(buf);
    int x = 0;
    int pos = 1;
    if (alpha) x--;
    for (int i=k-1; i>=0; i--) {
        int index = strchr(dict, buf[i])-dict;
        if (alpha) index++;
        x += index*pos;
        pos *= n;
    }
    return x;
}

int main() {
    char dict[] = "abc";
    char buf1[256];
    char buf2[256];
    for (int i=0; i<20; i++) {
        conv(i, dict, buf1, 0);
        conv(i, dict, buf2, 1);
        int x = rconv(buf1, dict, 0);
        int y = rconv(buf2, dict, 1);
        cout << i << "\t"
            << buf1 << "\t" << x << "\t"
            << buf2 << "\t" << y << "\t" << endl;
    }
}