#include <stdio.h>
#include <stdint.h>
#include <stdbool.h>
#include <stdlib.h>
#include <math.h>

#define DEFAULT_FILE    "input.txt"
#define STRBUF_LEN      200
#define ISDIGIT(X)      (X >= '0' && X <= '9')

#define NUM_RACES       4

uint64_t parse_num(char *str)
{
    uint64_t num = 0;
    while (ISDIGIT(*str))
    {
        num = (num * 10) + (*str - '0');
        str++;
    }
    return num;
}

void parse_line(char *str, uint16_t *nums)
{
    uint16_t race = 0;

    for (race = 0; race < NUM_RACES; race++)
    {
        while (!ISDIGIT(*str)) str++;
        nums[race] = parse_num(str);
        while (ISDIGIT(*str)) str++;
    }
}

// Solves for the 0-intersection points, placing the results in result1 and result2.
// Returns true if it can be solved, returns false if it is unsolvable.
bool solve_quadratic(uint64_t time, uint64_t distance, uint64_t *result1, uint64_t *result2)
{
    double doubleres1;
    double doubleres2;
    int64_t s = (time * time) - (4 * distance);
    if (s < 0) return false;
    doubleres1 = ( time - sqrt(s) ) / 2;
    doubleres2 = ( time + sqrt(s) ) / 2;

    if (doubleres1 == (double)(ceil(doubleres1))) doubleres1 += 1;
    *result1 = ceil(doubleres1);

    if (doubleres2 == (double)(floor(doubleres2))) doubleres2 -= 1;
    *result2 = floor(doubleres2);
    return true;
}

int main(int argc, char **argv)
{
    // Get filename as an argument, if there is one
    char *path = (argc > 1) ? argv[1] : DEFAULT_FILE;

    if (!path)
    {
        printf("Requires input file.\n");
        return 1;
    }

    FILE *file = fopen(path, "r");
    char strbuf[STRBUF_LEN] = {0};

    if (!file)
    {
        printf("Could not find file.");
        return 1;
    }

    uint16_t times[NUM_RACES] = {0};
    uint16_t dists[NUM_RACES] = {0};
    uint16_t results[NUM_RACES] = {0};

    fgets(strbuf, STRBUF_LEN, file);
    parse_line(strbuf, times);

    fgets(strbuf, STRBUF_LEN, file);
    parse_line(strbuf, dists);

    uint16_t i = 0;
    uint64_t multiplied = 1;

    for (i = 0; i < NUM_RACES; i++)
    {
        uint64_t res1;
        uint64_t res2;
        if (!solve_quadratic(times[i], dists[i], &res1, &res2))
        {
            printf("Error?? Invalid quadratic.\n");
            return 1;
        }

        results[i] = res2 - res1 + 1;
        printf("%d ", results[i]);
        multiplied *= results[i];
    }

    printf("\nMultiplied: %lu\n", multiplied);

    return 0;
}