AoC2024/3/main.c

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

#define LINES 1000

struct instruction {
	char *coord;
	struct instruction *next;
};

void addInstruction(struct instruction *start, char *coord)
{
	// traverse list until last member
	while(start->next) start = start->next;
	
	// allocate and store ptr
	start->next = malloc(sizeof(struct instruction));
	
	// store coords in new item
	start->next->coord = coord;
	start->next->next = 0;
}

bool confirm_numbers(char *start, char *end) {
	for (int i = 0; (start[i] >= '0' && start[i] <= '9') || start[i] == ','; i++) {
		if (start[i + 1 ] == ')')
			return 1;
	}
	return 0;
}

int parse_numbers(char *string)
{
	int i = 0;
	int a = 0;
	int b = 0;
	while (string[i] >= '0' && string[i] <= '9') {
		a = a * 10 + string[i] - '0';
		i++;
	}
	// skip comma!
	i++;
	while (string[i] >= '0' && string[i] <= '9') {
		b = b * 10 + string[i] - '0';
		i++;
	}
	return a * b;
}

int main()
{
	unsigned int sum = 0;
	char instructions[32];
	
	FILE *input;
	input = fopen("./input", "r");

	fseek(input, 0L, SEEK_END);
	unsigned int fLen = ftell(input);
	char *memory = malloc(fLen * sizeof(char) + 1);

	rewind(input);
	fread(memory, fLen, sizeof(char), input);
	memory[fLen + 1] = '\0';
	fclose(input);
	
	// find first instruction start for the list head
	char *start = memory;
	start = strstr(start, "mul(") + 4;
	struct instruction *list = malloc(sizeof(struct instruction));
	list->coord = start;
	list->next = 0;

	// find the rest of the instructions and append to the linked list
	while (start = strstr(start, "mul(")) {
		start = start + 4;
		// confirm format %d,%d)
		if (confirm_numbers(start, memory + fLen))
			addInstruction(list, start);
	}

	// from each instruction start, parse and mult numbers
	struct instruction *current = list;
	while (current) {
		sum += parse_numbers(current->coord);
		current = current->next;
	}

	printf("%d\n", sum);
}