adventofcode2022/day25/snafu.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define BUFFER_SIZE 64
#define MAGIC_NUMBER 5

long powNum(long, long);
long snafu_to_human(char*, int);
void human_to_snafu(char*, long);

int main() {
    char buf[BUFFER_SIZE], *p, c;
    memset(buf, 0, BUFFER_SIZE);
    p = buf;
    long sum = 0;

    while ((c = getchar()) != EOF) {
        *p++ = c;
        if (c == '\n') {
            sum += snafu_to_human(p-2, p-buf);
            memset(buf, 0, BUFFER_SIZE);
            p = buf;
        }
    }

    printf("Sum in decimal: %li\n", sum);
    char snafu[64];
    memset(snafu, 0, 64);
    human_to_snafu(snafu, sum);
    printf("Sum in SNAFU: %s\n", snafu);
}

long powNum(long b, long e) {
    long result = 1;
    for (int i = 0; i < e; i++) {
        result *= b;
    }

    return result;
}

long snafu_to_human(char* p, int len) {
    long result = 0;
    for (int i = 0; i < len; i++) {
        switch(*(p-i)) {
            case '0':
                break;
            case '1':
                result += powNum(MAGIC_NUMBER, i);
                break;
            case '2':
                result += 2*powNum(MAGIC_NUMBER, i);
                break;
            case '-':
                result += -powNum(MAGIC_NUMBER, i);
                break;
            case '=':
                result += -2*powNum(MAGIC_NUMBER, i);
                break;
        }
    }

    return result;
}

void human_to_snafu(char* p, long decimal) {
    char buf[64], *q;
    memset(buf, 0, 64);

    long num = decimal;
    int len = 0;
    int remainder = 0;

    while (num != 0) {
        int numeric = num % MAGIC_NUMBER;
        num /= MAGIC_NUMBER;
        numeric += remainder;
        remainder = 0;
        if (numeric > 2) {
            remainder = 1;
            numeric = numeric - MAGIC_NUMBER;
        }
        if (numeric == -1) {
            buf[len] = '-';
        } else if (numeric == -2) {
            buf[len] = '=';
        } else {
            buf[len] = '0' + numeric;
        }
        len++;
    }

    if (remainder) {
        buf[len] = '1';
        len++;
    }

    for (int i = 0; i <= len; i++) {
        *(p+len-i-1) = buf[i];
    }
}