advent_of_code/day5/c/aoc_day5.c

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

/* #define DEBUG */

#define INPUT_FILE ("../input.txt")
#define NUM_EDGES (500)
#define MAX_DIM (1000)

/* #define INPUT_FILE ("../input_test.txt") */
/* #define NUM_EDGES (10) */
/* #define MAX_DIM (10) */

typedef struct vertex_t
{
	int x;
	int y;
}vertex_t;

typedef struct edge_t
{
	vertex_t a;
	vertex_t b;
}edge_t;

// takes an array of edges and the length
// fills a grid according to part 1 rules
// computes overlapping points and returns this
int d5_part1(edge_t* edges, int len);

// takes an array of edges and the length
// fills a grid according to part 1 rules
// computes overlapping points and returns this
int d5_part2(edge_t* edges, int len);

int calc_overlapping_points(int _grid[MAX_DIM][MAX_DIM], size_t dimension);
void print_grid(int _grid[MAX_DIM][MAX_DIM], size_t dimension);

int main(void)
{
	edge_t edges[NUM_EDGES];
	memset(edges, 0, sizeof(edge_t) * NUM_EDGES);

	FILE* fp = fopen(INPUT_FILE, "r");
	if(fp == NULL)
	{
		printf("open file error...\n");
		exit(-1);
	}

	int edge_ct = 0;

	size_t len = 0;
	ssize_t rc = 0;
	char* line = NULL;

	while((rc = getline(&line, &len, fp)) != -1)
	{
		if (edge_ct >= NUM_EDGES)
		{
			printf("edges[] out of bounds -- edge count: %d\n", edge_ct);
		}
		sscanf(line,
			   "%d,%d -> %d,%d",
			   &edges[edge_ct].a.x, &edges[edge_ct].a.y,
			   &edges[edge_ct].b.x, &edges[edge_ct].b.y);
#ifdef DEBUG
		printf("%d,%d -> %d,%d\n",
			   edges[edge_ct].a.x, edges[edge_ct].a.y,
			   edges[edge_ct].b.x, edges[edge_ct].b.y);
#endif
		edge_ct++;
	}
	printf("Overlapping points (part 1): %d\n", d5_part1(edges, NUM_EDGES));
	printf("Overlapping points (part 2): %d\n", d5_part2(edges, NUM_EDGES));
	return 0;
}

// takes an array of edges and the length
// fills a grid according to part 1 rules
// computes overlapping points and returns this
int d5_part1(edge_t* edges, int len)
{
	int grid[MAX_DIM][MAX_DIM];
	memset(grid, 0, MAX_DIM * MAX_DIM * sizeof(int));

	for(int edge = 0; edge < len; edge++)
	{
		if(edges[edge].b.x == edges[edge].a.x)
		{
			// from y2 to y1
			if(edges[edge].a.y > edges[edge].b.y)
			{
				for(int ind = edges[edge].b.y; ind <= edges[edge].a.y; ind++)
				{
					grid[edges[edge].a.x][ind]++;
				}
			}
			else // from y1 to y2
			{
				for(int ind = edges[edge].a.y; ind <= edges[edge].b.y; ind++)
				{
					grid[edges[edge].a.x][ind]++;
				}
			}
		}
		else if(edges[edge].b.y == edges[edge].a.y)
		{
			if(edges[edge].a.x > edges[edge].b.x)
			{
				// 
				for(int ind = edges[edge].b.x; ind <= edges[edge].a.x; ind++)
				{
					grid[ind][edges[edge].a.y]++;
				}
			}
			else
			{
				for(int ind = edges[edge].a.x; ind <= edges[edge].b.x; ind++)
				{
					grid[ind][edges[edge].a.y]++;
				}
			}
		}
	}

#ifdef DEBUG
	printf("Part 1 grid:\n");
	print_grid(grid, MAX_DIM);
#endif
	return calc_overlapping_points(grid, MAX_DIM);
}
// takes an array of edges and the length
// fills a grid according to part 1 rules
// computes overlapping points and returns this
int d5_part2(edge_t* edges, int len)
{
	int grid[MAX_DIM][MAX_DIM];
	memset(grid, 0, MAX_DIM * MAX_DIM * sizeof(int));
	for(int edge = 0; edge < len; edge++)
	{
		// now we have to account for horizontal, vertical, and diagonal lines, or lines with a 45 degree angle
		// this just means the slope must be 1. so y2-y1/x2-x1 needs to be 1
		if(edges[edge].b.x == edges[edge].a.x)
		{
			// from y2 to y1
			if(edges[edge].a.y > edges[edge].b.y)
			{
				for(int ind = edges[edge].b.y; ind <= edges[edge].a.y; ind++)
				{
					grid[edges[edge].a.x][ind]++;
				}
			}
			else // from y1 to y2
			{
				for(int ind = edges[edge].a.y; ind <= edges[edge].b.y; ind++)
				{
					grid[edges[edge].a.x][ind]++;
				}
			}
		}
		else if(edges[edge].b.y == edges[edge].a.y)
		{
			if(edges[edge].a.x > edges[edge].b.x)
			{
				// 
				for(int ind = edges[edge].b.x; ind <= edges[edge].a.x; ind++)
				{
					grid[ind][edges[edge].a.y]++;
				}
			}
			else
			{
				for(int ind = edges[edge].a.x; ind <= edges[edge].b.x; ind++)
				{
					grid[ind][edges[edge].a.y]++;
				}
			}
		}
		else if(abs(edges[edge].b.y - edges[edge].a.y) ==
				abs(edges[edge].b.x - edges[edge].a.x))
		{
			int inc_x = (edges[edge].b.x - edges[edge].a.x) /
				abs(edges[edge].b.x - edges[edge].a.x);
			int inc_y = (edges[edge].b.y - edges[edge].a.y) /
				abs(edges[edge].b.y - abs(edges[edge].a.y));
			int distance = abs(edges[edge].b.x - edges[edge].a.x);
			vertex_t start =
			{
				.x = edges[edge].a.x,
				.y = edges[edge].a.y
			};
			for(int ind = 0; ind <= distance; ind++)
			{
				grid[start.x][start.y]++;
				start.x += inc_x;
				start.y += inc_y;
			}

		}
	}
#ifdef DEBUG
	print_grid(grid, MAX_DIM);
#endif
	return calc_overlapping_points(grid, MAX_DIM);
}

int calc_overlapping_points(int _grid[MAX_DIM][MAX_DIM], size_t dimension)
{
	int ret = 0;
	for(int i = 0; i < (int)dimension; i++)
	{
		for(int j = 0; j < (int)dimension; j++)
		{
			if(_grid[i][j] > 1)
			{
				ret++;
			}
		}
	}
	return ret;
}

void print_grid(int _grid[MAX_DIM][MAX_DIM], size_t dimension)
{
	printf("  |");
	for(int i = 0; i < (int)dimension; i++)
	{
		printf("%2d ", i);
	}
	printf("\n");
	for(int i = 0; i < (int)dimension; i++)
	{
		printf("%d | ", i);
		for(int j = 0; j < (int)dimension; j++)
		{
			if(_grid[j][i] < 1)
			{
				printf("%-2s ", ".");
			}
			else
			{
				printf("%-2d ", _grid[j][i]);
			}
		}
		printf("\n");
	}
}