advent_of_code/day3/c/aoc_day3.c

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


#define ARR_LEN (1000)
#define BIT_AMOUNT (12)
#define INPUT_FILE ("input.txt")
#define BIT_MASK (0xFFF)

// read file, dump into diagnostics and count bits
void d3_init(int* diagnostics, size_t diag_len,
			int* bit_ct, size_t bit_ct_len);

// return answer for part one
int d3_part_one(int* diagnostics, size_t diag_len,
			int* bit_ct, size_t bit_ct_len);

// returns answer for part two
int d3_part_two(const int* const diagnostics, size_t diag_len);



// if binary we're assuming bit size is 12 because this project is specific to 12 bit numbers
static void print_arr(const int* const arr, size_t len, bool binary)
{
	if(binary)
	{
		printf("\n");
		for(int ind = 0; ind < len; ind++)
		{
			printf("[%d]: ", ind);
			for(int bit = BIT_AMOUNT - 1; bit >= 0; bit--)
			{
				printf("%d", ((arr[ind] & (1 << bit))>>bit));
			}
			printf("\n");
		}
	}
	else
	{
		for(int ind = 0; ind < len; ind++)
		{
			printf("[%d]: %d\n", ind, arr[ind]);
		}
	}
}

int main(int argc, char** argv)
{
	int diagnostic_arr[ARR_LEN];
	int bit_ct[BIT_AMOUNT];

	memset(diagnostic_arr, 0, ARR_LEN * sizeof(int));
	memset(bit_ct, 0, BIT_AMOUNT * sizeof(int));

	d3_init(diagnostic_arr, ARR_LEN, bit_ct, BIT_AMOUNT);

	int power_consumption = d3_part_one(diagnostic_arr, ARR_LEN, bit_ct, BIT_AMOUNT);
	printf("(Part 1 Answer) Power Consumption: %d\n", power_consumption);

	int life_support_rating = d3_part_two(diagnostic_arr, ARR_LEN);
	printf("(Part 2 Answer) Life support rating: %d\n", life_support_rating);

	return 0;
}


// read file, dump into diagnostics and count bits
void d3_init(int* diagnostics, size_t diag_len,
			int* bit_ct, size_t bit_ct_len)
{

	FILE* fp = fopen(INPUT_FILE, "r");
	if(!fp)
	{
		printf("Failed to open file for reading...\n");
		exit(-1);
	}
	char* line = NULL;
	size_t len = 0;
	for(int ind = 0; ind < ARR_LEN; ind++)
	{
		ssize_t rc = getline(&line, &len, fp);
		if(rc == -1)
		{
			printf("EXITING ABNORMALLY\n");
			exit(-1);
		}
		diagnostics[ind] = strtol(line, NULL, 2);
		for(int bit = 0; bit < BIT_AMOUNT; bit++)
		{
			printf("%d", (diagnostics[ind] & (1<<bit))>>bit);
			bit_ct[bit] += ((diagnostics[ind] & (1 << bit))>>bit);
		}
		printf("\n");
	}

	fclose(fp);
}

// returns status of init
int d3_part_one(int* diagnostics, size_t diag_len,
			int* bit_ct, size_t bit_ct_len)
{
	int gamma = 0;
	int epsilon = 0;
	for(int bit = 0; bit < bit_ct_len; bit++)
	{
		gamma += ((bit_ct[bit] > (ARR_LEN >> 1))<<bit);
	}
	epsilon = (~gamma) & BIT_MASK;
	printf("Epsilon: %d\t gamma: %d\n", epsilon, gamma);
	return gamma * epsilon;
}

// returns answer for part two
// we can use the answer from part 1 to cut out a lot of unnecessary instructions
int d3_part_two(const int* const diagnostics, size_t diag_len)
{
	int o2_gen_rating = 0;
	int co2_scrubber_rating = 0;
	int ans = 0;
	// alternating active buffers
	int diag_copy[2][ARR_LEN + 1];

	// we copy diagnostics into our second diag_copy arr
	// this way we start with diag_copy[0] being zeroed
	// and diag_copy[1] having our original data.
	// from there we will go back and forth, filtering data
	// from eachother
	memcpy(&diag_copy[(~(BIT_AMOUNT - 1)%2) & 0x01], diagnostics, diag_len * sizeof(int));

	// last value will be active count, i.e. how many vars are actually in the array
	diag_copy[(BIT_AMOUNT - 1)%2][ARR_LEN] = 0;
	diag_copy[(~(BIT_AMOUNT - 1)%2) & 0x01][ARR_LEN] = ARR_LEN;

	// finding oxygen generator rating
	for(int bit = BIT_AMOUNT - 1; bit >= 0; bit--)
	{
		int* ctr_write = &diag_copy[bit%2][ARR_LEN];
		int* ctr_read = &diag_copy[~(bit%2) & 0x01][ARR_LEN];

		int* diag_write = diag_copy[bit%2];
		const int* diag_read = diag_copy[~(bit%2) & 0x01];

		memset(diag_write, 0, (sizeof(int) * ARR_LEN) + sizeof(int));

		volatile int bit_ct = 0;
		for(int ind = 0; ind < *ctr_read; ind++)
		{
			if((diag_read[ind] >> bit) & 0x01)
			{
				bit_ct++;
			}
		}

		for(int ind = 0; ind < *ctr_read; ind++)
		{
			if(bit_ct >= (*ctr_read - bit_ct))
			{
				if((diag_read[ind] >> bit) & 0x01)
				diag_write[(*ctr_write)++] = diag_read[ind];
			}
			else
			{
				if(!((diag_read[ind] >> bit) & 0x01))
				{
					diag_write[(*ctr_write)++] = diag_read[ind];
				}
			}
		}
		if(*ctr_write <= 1)
		{
			printf("found o2 rating\n");
			o2_gen_rating = diag_write[*ctr_write-1];
			break;
		}
	}


	printf("o2 rating: %d\n", o2_gen_rating);

	// now we need to do a similar thing for co2 scubber rating
	// this time we want to find the least common bit instead of most common bit

	// we copy diagnostics into our second diag_copy arr
	// this way we start with diag_copy[0] being zeroed
	// and diag_copy[1] having our original data.
	// from there we will go back and forth, filtering data
	// from eachother
	memcpy(&diag_copy[(~(BIT_AMOUNT - 1)%2) & 0x01], diagnostics, diag_len * sizeof(int));

	// last value will be active count, i.e. how many vars are actually in the array
	diag_copy[(BIT_AMOUNT - 1)%2][ARR_LEN] = 0;
	diag_copy[(~(BIT_AMOUNT - 1)%2) & 0x01][ARR_LEN] = ARR_LEN;

	// finding oxygen generator rating
	for(int bit = BIT_AMOUNT - 1; bit >= 0; bit--)
	{
		int* ctr_write = &diag_copy[bit%2][ARR_LEN];
		int* ctr_read = &diag_copy[~(bit%2) & 0x01][ARR_LEN];

		int* diag_write = diag_copy[bit%2];
		const int* diag_read = diag_copy[~(bit%2) & 0x01];

		memset(diag_write, 0, (sizeof(int) * ARR_LEN) + sizeof(int));

		int bit_ct = 0;
		for(int ind = 0; ind < *ctr_read; ind++)
		{
			if((diag_read[ind] >> bit) & 0x01)
			{
				bit_ct++;
			}
		}

		for(int ind = 0; ind < *ctr_read; ind++)
		{
			if(bit_ct < (*ctr_read - bit_ct))
			{
				if((diag_read[ind] >> bit) & 0x01)
				diag_write[(*ctr_write)++] = diag_read[ind];
			}
			else
			{
				if(!((diag_read[ind] >> bit) & 0x01))
				{
					diag_write[(*ctr_write)++] = diag_read[ind];
				}
			}
		}
		if(*ctr_write <= 1)
		{
			printf("found co2 \n");
			co2_scrubber_rating = diag_write[*ctr_write-1];
			break;
		}
	}

	printf("o2 gen rating: %d\nco2 scrubber rating: %d\n", o2_gen_rating, co2_scrubber_rating);
	return co2_scrubber_rating * o2_gen_rating;
}