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#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <malloc.h>
#include <string.h>
#define MAX_INPUT_WIDTH 128
#define MAX_INPUT_HEIGTH 128
#define MAX_INPUT MAX_INPUT_WIDTH * MAX_INPUT_HEIGTH
int count_char(const char *source, char search)
{
int oc = 0;
do {
oc += *source == search;
} while (*++source);
return oc;
}
void replace_char(char *destination, const char *source, char original, char replace)
{
do {
if (*source == original) {
*destination = replace;
}
else {
*destination = *source;
}
} while (++destination && *++source);
*destination = 0;
}
int sur_oc_seats(const char *source, size_t width, size_t height, size_t index_y, size_t index_x)
{
int num = 0;
// Check 3 seats on the line above
if (index_y > 0) {
size_t x = index_x == 0 ? index_x : index_x - 1;
size_t end_x = index_x < width - 1 ? index_x + 2 : index_x + 1;
for (; x < end_x; x++) {
num += source[(index_y - 1) * width + x] == '#';
}
}
// Check sides
if (index_x > 0) {
num += source[index_y * width + index_x - 1] == '#';
}
if (index_x < width - 1) {
num += source[index_y * width + index_x + 1] == '#';
}
// Check 3 seats on the line above
if (index_y < height - 1) {
size_t x = index_x == 0 ? index_x : index_x - 1;
size_t end_x = index_x < width - 1 ? index_x + 2 : index_x + 1;
for (; x < end_x; x++) {
num += source[(index_y + 1) * width + x] == '#';
}
}
return num;
}
int solve(const char *filename)
{
FILE *file = fopen(filename, "r");
// Include space for newline and string terminator
char buffer[128] = { 0 };
char input[MAX_INPUT] = { 0 };
size_t height = 1;
fgets(buffer, 128, file);
size_t width = strchr(buffer, '\n') - buffer;
replace_char(input, buffer, 'L', '#');
while (fgets(buffer, 128, file)) {
// Round 1
replace_char(&input[height++ * width], buffer, 'L', '#');
}
fclose(file);
size_t size = height * width;
// Zero terminate
input[size] = 0;
char input2[MAX_INPUT] = { 0 };
do {
for (size_t i = 0; i < size; i++) {
if (input[i] == '.') {
input2[i] = '.';
}
else if (input[i] == 'L') {
if (sur_oc_seats(input, width, height, i / width, i % width) == 0) {
input2[i] = '#';
}
else {
input2[i] = 'L';
}
}
else if (input[i] == '#') {
if (sur_oc_seats(input, width, height, i / width, i % width) >= 4) {
input2[i] = 'L';
}
else {
input2[i] = '#';
}
}
}
} while (memcmp(input, input2, size) && memcpy(input, input2, size));
return count_char(input, '#');
}
int main(int argc, char *argv[])
{
printf("%i\n", solve(argv[argc - 1]));
}
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