130 lines
3.4 KiB
C
130 lines
3.4 KiB
C
#include <assert.h>
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#include <stdlib.h>
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#include <stdbool.h>
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#include <string.h>
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#include <inttypes.h>
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#include <stdio.h>
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#include <math.h>
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#include "common.c"
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/// This one is the "smart" one, instead of doing a full scan of the
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/// grid, a FIFO of points to fire is kept up to date each time a cell
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/// is firered. Sadly "smart" is not smart.
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typedef struct point {
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int x;
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int y;
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} point_t;
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typedef struct todo {
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int width;
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int height;
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int size;
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int idx;
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int qty;
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point_t *points;
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bool *dedup; // Used to avoid adding twice the same point, stored as x*width+y
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} todo_t;
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// The todo is deduplicated list of points.
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todo_t *todo_new(size_t width, size_t height)
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{
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todo_t *todo = malloc(sizeof(*todo));
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todo->qty = 0;
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todo->width = width;
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todo->height = height;
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todo->size = width * 4;
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todo->dedup = calloc(todo->width * todo->height, sizeof(bool));
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todo->points = malloc(todo->size * sizeof(point_t));
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return todo;
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}
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static void todo_write(todo_t *todo, point_t point)
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{
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if (todo->dedup[point.x * todo->width + point.y])
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return;
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if (todo->qty == todo->size - 1) {
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todo->points = realloc(todo->points, sizeof(point_t) * todo->size * 2);
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todo->size *= 4;
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}
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todo->dedup[point.x * todo->width + point.y] = true;
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todo->points[todo->qty] = point;
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todo->qty += 1;
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}
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static point_t todo_read(todo_t *todo)
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{
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assert(todo->qty > 0);
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todo->qty -= 1;
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todo->dedup[todo->points[todo->qty].x * todo->width + todo->points[todo->qty].y] = false;
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return todo->points[todo->qty];
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}
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void unstable_to_todo(int width, int **terrain, todo_t *todo)
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{
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for (int x = 0; x < width; x++)
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for (int y = 0; y < width; y++)
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if (terrain[x][y] >= 4)
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todo_write(todo, (point_t){x, y});
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}
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void apply_gravity(int width, int **terrain)
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{
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int div;
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todo_t *todo;
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point_t point;
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unsigned int collapses = 0;
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todo = todo_new(width, width);
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unstable_to_todo(width, terrain, todo);
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while (todo->qty) {
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point = todo_read(todo);
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collapses += 1;
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div = terrain[point.x][point.y] / 4;
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terrain[point.x][point.y] %= 4;
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terrain[point.x - 1][point.y] += div;
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terrain[point.x + 1][point.y] += div;
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terrain[point.x][point.y + 1] += div;
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terrain[point.x][point.y - 1] += div;
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if (terrain[point.x - 1][point.y] >= 4)
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todo_write(todo, (point_t){point.x-1, point.y});
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if (terrain[point.x + 1][point.y] >= 4)
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todo_write(todo, (point_t){point.x+1, point.y});
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if (terrain[point.x][point.y + 1] >= 4)
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todo_write(todo, (point_t){point.x, point.y+1});
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if (terrain[point.x][point.y - 1] >= 4)
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todo_write(todo, (point_t){point.x, point.y-1});
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}
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}
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int **sandpile_new(int width)
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{
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int **terrain = calloc(width, sizeof(int*));
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int *data = calloc(width * width, sizeof(int));
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for (int i = 0; i < width; i++) {
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terrain[i] = data + i * width;
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}
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return terrain;
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}
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int main(int argc, char **argv)
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{
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args args = {0};
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if (parse_args(argc, argv, &args))
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return EXIT_FAILURE;
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int width = sandpile_width(args.height);
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int **terrain = sandpile_new(width);
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terrain[width / 2][width / 2] = args.height;
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apply_gravity(width, terrain);
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save_terrain(width, terrain, &args);
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return EXIT_SUCCESS;
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}
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