Advent-of-Code/2021/day5/solution-part2.c

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


#define MAX(a, b) ((a) < (b) ? (b) : (a))
#define MIN(a, b) ((a) < (b) ? (a) : (b))

void printGrid(unsigned int maxx, unsigned int maxy, unsigned int grid[maxx+1][maxy+1]){
	for( unsigned int y = 0; y <= maxy; y++ ){
		for( unsigned int x = 0; x <= maxx; x++ ){
			printf("%3i", grid[x][y]);
		}
		printf("\n");
	}
}

int main( int argc, char *argv[] ){
	if( argc == 2 ) {


		FILE *fp=fopen(argv[1], "r");

		unsigned int maxx=0, maxy=0;

		while (!feof (fp)){
			int x1=0,x2=0,y1=0,y2=0;

			fscanf(fp, "%i,%i -> %i,%i\n", &x1,&y1,&x2,&y2);

			maxx= MAX( maxx, MAX( x1, x2 ) );
			maxy= MAX( maxy, MAX( y1, y2 ) );

		}



		unsigned int grid[maxx+1][maxy+1];
		memset( &grid, 0, (maxx+1)*(maxy+1)*sizeof(int) );

		rewind(fp);

		unsigned int cellsWithOverlap=0;

		unsigned int iteration = 0;
		while (!feof (fp)){
			int x1=0,x2=0,y1=0,y2=0;

			fscanf(fp, "%i,%i -> %i,%i\n", &x1,&y1,&x2,&y2);

			//printf("Iteration: %i\n", iteration);


			if ( x1 == x2 ){ // Virtical lines
				for( unsigned int y = MIN(y1,y2); y<=MAX(y1,y2); y++ )
					if ( 1 == grid[x1][y]++) cellsWithOverlap++;
			} else if ( y1 == y2 ){ // Horisontal lines
				for( unsigned int x = MIN(x1,x2); x<=MAX(x1,x2); x++ )
					if ( 1 == grid[x][y1]++) cellsWithOverlap++;
			} else { // Diaganal lines
				// Since we know all diagonals are 45 deg we only need to worry about if this is 1 or -1
				int dx = (x2 - x1) / abs(x2 - x1);
				int dy = (y2 - y1) / abs(y2 - y1);
				for (unsigned int i = 0; i <= MAX(x1,x2) - MIN(x1,x2); i++){
					unsigned int x = x1 + ( dx * i );
					unsigned int y = y1 + ( dy * i );
					if ( 1 == grid[x][y]++) cellsWithOverlap++;
				}

			}

			iteration++;
		}

		printf("%i cells with overlap\n", cellsWithOverlap);


		//printGrid(maxx, maxy, grid);

		fclose(fp);




		return 0;
	} else {
		printf("You need to provide a file\n");
		return 1;
	}
}