bestbefore

bestbefore.c

/* http://www.spotify.com/us/jobs/tech/best-before/ */

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

char* process_raw(char *p);
char* process(char *pa, char *pb, char *pc);
char* process4(int *len ,int *num, size_t n);
char* process2(int *len ,int *num, size_t n);
void sort(int *arr, int *aux, size_t len);
void swap(int *arr, size_t i, size_t j);
int chkdate(int y, int m, int d);

int main(int argc, char **argv)
{
	char buf[16] = {0};
	char raw[16];
	char *out = NULL;
	int ret = scanf("%s", buf);
	if (ret != 1) {
		fprintf(stderr, "%s\n", "bad input");
		return -1;
	}
	
	memcpy(raw, buf, sizeof(buf));
	out = process_raw(buf);
	if (out == NULL) {
		printf("%s is illegal", raw);
	}
	else {
		printf("%s", out);
		free(out);
	}

	return 0;
}

char* process_raw(char *p)
{
	char *pa, *pb, *pc;
	char *best = NULL;

	if (p == NULL)
		return NULL;
	
	pa = p;
	pb = strchr(p, '/');
	if (pb)
		*pb++ = '\0';
	pc = strchr(pb, '/');
	if (pc)
		*pc++ = '\0';
	assert(pa && pb && pc);

	return process(pa, pb, pc);
}

char* process(char *pa, char *pb, char *pc)
{
	int num[3];
	int len[3];

	num[0] = atoi(pa);
	num[1] = atoi(pb);
	num[2] = atoi(pc);

	len[0] = strlen(pa);
	len[1] = strlen(pb);
	len[2] = strlen(pc);
	
	/* sort by length, descending */
	sort(len, num, 3);
	if (len[0] == 4 && len[1] < 3) {
		return process4(len, num, 3);
	} else if (len[0] < 3) {
		return process2(len, num, 3);
	}

	return NULL;
}

void sort(int *arr, int *aux, size_t len)
{
	size_t i, j;
	for (i = 0; i < len ; i++) {
		for (j = i + 1; j < len; j++) {
			if (arr[i] < arr[j]) {
				swap(arr, i, j);
				swap(aux, i, j);
			}
		}
	}
}

void swap(int *arr, size_t i, size_t j)
{
	int x = arr[i];
	arr[i] = arr[j];
	arr[j] = x;
}

char* process4(int *len ,int *num, size_t n)
{
	int y, m, d;
	int valid;

	if (num[0] > 2999 || num[0] < 2000) {
			return NULL;
	}

	/* sort by value, descending */
	sort(num, len, 3);
	if (num[2] > 12 || num[1] < 1 || num[2] < 1) {
		return NULL;
	}

	y = num[0];
	m = num[2];
	d = num[1];
	valid =chkdate(y, m, d);
	if (valid) {
		char *p = malloc(11);
		if (p) {
			sprintf(p, "%04d-%02d-%02d", y, m, d);
			return p;
		}
	}
	
	return NULL;
}

char* process2(int *len ,int *num, size_t n)
{
	int num1[3], len1[3];
	char *p = NULL;

	/* sort by value, descending */
	sort(num, len, 3);

	memcpy(num1, num, sizeof(num1));
	memcpy(len1, len ,sizeof(len1));
	num1[2] += 2000;
	sort(num1, len1, 3);
	p = process4(len1, num1, 3);
	if (!p) {
		memcpy(num1, num, sizeof(num1));
		memcpy(len1, len ,sizeof(len1));
		num1[1] += 2000;
		sort(num1, len1, 3);
		p = process4(len1, num1, 3);
		if (!p) {
			memcpy(num1, num, sizeof(num1));
			memcpy(len1, len ,sizeof(len1));
			num1[0] += 2000;
			sort(num1, len1, 3);
			return process4(len1, num1, 3);
		}
	}

	return p;
}

int chkdate(int y, int m, int d)
{
	static int lookup[13] = { 0,
		31, 28, 31, 30, 31, 30,
		31, 31, 30, 31, 30, 31
	};
	int fix;

	if (y % 400 == 0)
		fix = 1;
	else if (y % 100 == 0)
		fix = 0;
	else if (y % 4 == 0)
		fix = 1;
	else
		fix = 0;
	
	if (m != 2 && lookup[m] >= d)
		return 1;
	if (m == 2 && lookup[m] + fix >= d)
		return 1;
	
	return 0;
}