Advent-of-Code/2021/day15/solution-part2.c

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

#define ANSI_COLOR_RED     "\x1b[31m"
#define ANSI_COLOR_YELLOW  "\x1b[33m"
#define ANSI_COLOR_RESET   "\x1b[0m"
#define ANSI_COLOR_BOLD   "\x1b[1m"

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

typedef struct Square Square;
typedef struct SquareList SquareList;

struct Square{
	unsigned int risk;
	Square *previous;
	unsigned int distanceFromStart;
	Square *up;
	Square *down;
	Square *left;
	Square *right;
	bool onShortestPath;
	bool used;
};

struct SquareList{
	Square *square;
	SquareList *next;
};

SquareList* newSqareListItem(Square *square){
	SquareList *newSquare = malloc(sizeof(SquareList));
	newSquare->square = square;
	newSquare->next = NULL;
	return newSquare;
}


int countRows(FILE *fp){
	unsigned int lines=0;

	while (EOF != (fscanf(fp, "%*[^\n]"), fscanf(fp,"%*c")))
		++lines;
	return lines;
}

int countCols(FILE *fp){
	unsigned int lineLength=0;
	char ch = fgetc(fp);
	while ( ch != '\n' ){
		lineLength++;
		ch = fgetc(fp);
	}
	return lineLength;
}

void printGrid( unsigned int cols, unsigned int rows, Square **grid){
	for ( unsigned int row = 0; row < rows; row++ ){
		if ( row % ( rows / 5 ) == 0 ) printf("\n");
		for ( unsigned int col = 0; col < cols; col++ ){
			if ( col % ( cols / 5 ) == 0 ) printf(" ");
			if ( grid[col][row].onShortestPath ) printf(ANSI_COLOR_RED);
			if ( col < cols / 5 && row < rows/5 ) printf(ANSI_COLOR_BOLD);
			printf("%i ", grid[col][row].risk);
			if ( grid[col][row].onShortestPath ) printf(ANSI_COLOR_RESET);
			if ( col < cols / 5 && row < rows/5 ) printf(ANSI_COLOR_RESET);
		}
		printf("\n");
	}
}

void maybeUpdate(Square *current, Square *adjacent, SquareList *lastEndItem){
	if ( adjacent == NULL ) return ;
	if ( current->distanceFromStart + adjacent->risk < adjacent->distanceFromStart ){
		adjacent->distanceFromStart = current->distanceFromStart + adjacent->risk;
		adjacent->previous = current;
		lastEndItem->next = newSqareListItem(adjacent);
	}
}

void markAdjacent(Square *current, SquareList *firstEndItem){
	SquareList *lastItem = firstEndItem;
	while ( lastItem->next != NULL ) lastItem = lastItem->next;

	unsigned int currentDistance = current->distanceFromStart;

	maybeUpdate(current, current->up, lastItem);
	if ( lastItem->next != NULL ) lastItem = lastItem->next;

	maybeUpdate(current, current->down, lastItem);
	if ( lastItem->next != NULL ) lastItem = lastItem->next;

	maybeUpdate(current, current->left, lastItem);
	if ( lastItem->next != NULL ) lastItem = lastItem->next;
	maybeUpdate(current, current->right, lastItem);
}

Square* getLowestEndScoredSquare( SquareList *current ){
	Square *lowest = current->square;
	while ( current != NULL ){
		if ( ( current->square->distanceFromStart < lowest->distanceFromStart ) ){
			lowest = current->square;
		}
		current = current -> next;
	}
	return lowest;
}

SquareList* pruneEndList( SquareList *first ){
	// First item is a sliphtly special case
	while ( first != NULL && first->square->used ){
		first = first->next;
	}
	if ( first == NULL ) return NULL;
	SquareList *previous = first;
	SquareList *current = first->next;
	while ( current != NULL ){
		while ( current->square->used ){
			previous->next = current->next;
			current = previous->next;
		}
		previous = current;
		current = current->next;
	}
	return first;
}

unsigned int endListLength( SquareList *current ){
	unsigned int count = 0;
	while ( current != NULL ){
		count++;
		current = current->next;
	}
	return count;
}


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


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

		unsigned int cols=countCols(fp);
		rewind(fp);
		unsigned int rows=countRows(fp);
		rewind(fp);

		Square **grid=(Square**)malloc( cols * 5 * sizeof(Square *));
		for(unsigned int i=0; i<=rows*5;i++) {
			grid[i]=(Square*)malloc( rows * 5 * sizeof(Square));
			memset(grid[i], 0, sizeof(Square) * rows * 5);
		}

		char ch;
		unsigned int row=0, col=0;
		while ( !feof(fp) && fscanf(fp, "%c", &ch) ){
			if ( ch == '\n' ){
				col = 0;
				row++;
				continue;
			}
			for (unsigned int j=0; j < 5; j++){
				for (unsigned int i=0; i < 5 ; i++){
					unsigned int realcol = col + (i*cols), realrow = row + (j*rows);
					grid[realcol][realrow].risk = (( ch - '0') + i + j )  % 9;
					if ( grid[realcol][realrow].risk == 0 ) grid[realcol][realrow].risk = 9;
					grid[realcol][realrow].distanceFromStart = ~0;
					grid[realcol][realrow].up = ( realrow > 0 ) ? &grid[realcol][realrow-1] : NULL;
					grid[realcol][realrow].down = ( realrow < rows*5 - 1 ) ? &grid[realcol][realrow+1] : NULL;
					grid[realcol][realrow].left = ( realcol > 0 ) ? &grid[realcol-1][realrow] : NULL;
					grid[realcol][realrow].right = ( realcol < cols*5 - 1 ) ? &grid[realcol+1][realrow] : NULL;
					grid[realcol][realrow].onShortestPath = false;
					grid[realcol][realrow].used = false;
				}
			}
			col++;
		}



		//grid[cols*5-1][rows*5-1].onShortestPath = true;
		//printGrid(cols*5, rows*5, grid);



		Square *current = &grid[0][0];
		SquareList *firstEndItem = newSqareListItem(current);
		unsigned int i = 0;
		while (true){
			markAdjacent(current, firstEndItem);
			current->used = true;
			if ( current == &grid[cols*5-1][rows*5-1] ) break;
			firstEndItem = pruneEndList(firstEndItem);
			current = getLowestEndScoredSquare(firstEndItem);
			i++;
		}

		//while ( firstEndItem != NULL ){
		//	firstEndItem->square->onShortestPath = true;
		//	printf("Risk: %i Length: %i\n", firstEndItem->square->risk, firstEndItem->square->distanceFromStart);
		//	firstEndItem = firstEndItem->next;
		//}

		unsigned long total = 0;

		while ( true ){
			current->onShortestPath = true;
			total += current->risk;
			if ( current != &grid[0][0] )
				current = current->previous;
			else
				break;
		}
		printGrid(cols*5, rows*5, grid);


		//printGrid(cols*5, rows*5, grid);
		//grid[0][0].distanceFromStart = 0;
		printf("Total risk: %lu\n", total - grid[0][0].risk);
		//markAdjacent(grid, 0, 0);


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