Initial commit

2020/day17/day17.c

@@ -0,0 +1,144 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define INPUT_SIZE 8
+#define SIZE 30 // = (size of the input + 6 for growth + 1 padding) * 2
+
+bool alive3(bool state[SIZE][SIZE][SIZE], int x, int y, int z) {
+  int neighbours_count = 0;
+  for (int i = -1; i <= 1; ++i) {
+    for (int j = -1; j <= 1; ++j) {
+      for (int k = -1; k <= 1; ++k) {
+        neighbours_count += state[x + i][y + j][z + k];
+      }
+    }
+  }
+  neighbours_count -= state[x][y][z];
+
+  if (state[x][y][z]) {
+    return (2 <= neighbours_count) && (neighbours_count <= 3);
+  }
+  return 3 == neighbours_count;
+}
+
+bool alive4(bool state[SIZE][SIZE][SIZE][SIZE], int x, int y, int z, int w) {
+  int neighbours_count = 0;
+  for (int i = -1; i <= 1; ++i) {
+    for (int j = -1; j <= 1; ++j) {
+      for (int k = -1; k <= 1; ++k) {
+        for (int l = -1; l <= 1; ++l) {
+          neighbours_count += state[x + i][y + j][z + k][w + l];
+        }
+      }
+    }
+  }
+  neighbours_count -= state[x][y][z][w];
+
+  if (state[x][y][z][w]) {
+    return (2 <= neighbours_count) && (neighbours_count <= 3);
+  }
+  return 3 == neighbours_count;
+}
+
+int part1(bool input[INPUT_SIZE][INPUT_SIZE]) {
+  bool state[SIZE][SIZE][SIZE] = {false};
+  bool new_state[SIZE][SIZE][SIZE] = {false};
+
+  for (int i = 0; i < INPUT_SIZE; ++i) {
+    for (int j = 0; j < INPUT_SIZE; ++j) {
+      state[SIZE / 2 + i][SIZE / 2 + j][SIZE / 2] = input[i][j];
+    }
+  }
+
+  for (int step = 0; step < 6; ++step) {
+    for (int x = 1; x < SIZE - 1; ++x) {
+      for (int y = 1; y < SIZE - 1; ++y) {
+        for (int z = 1; z < SIZE - 1; ++z) {
+          new_state[x][y][z] = alive3(state, x, y, z);
+        }
+      }
+    }
+    memcpy(state, new_state, sizeof(state));
+  }
+
+  int active_count = 0;
+  for (int x = 1; x < SIZE - 1; ++x) {
+    for (int y = 1; y < SIZE - 1; ++y) {
+      for (int z = 1; z < SIZE - 1; ++z) {
+        active_count += state[x][y][z];
+      }
+    }
+  }
+  return active_count;
+}
+
+int part2(bool input[INPUT_SIZE][INPUT_SIZE]) {
+  bool state[SIZE][SIZE][SIZE][SIZE] = {false};
+  bool new_state[SIZE][SIZE][SIZE][SIZE] = {false};
+
+  for (int i = 0; i < INPUT_SIZE; ++i) {
+    for (int j = 0; j < INPUT_SIZE; ++j) {
+      state[SIZE / 2 + i][SIZE / 2 + j][SIZE / 2][SIZE / 2] = input[i][j];
+    }
+  }
+
+  for (int step = 0; step < 6; ++step) {
+    for (int x = 1; x < SIZE - 1; ++x) {
+      for (int y = 1; y < SIZE - 1; ++y) {
+        for (int z = 1; z < SIZE - 1; ++z) {
+          for (int w = 1; w < SIZE - 1; ++w) {
+            new_state[x][y][z][w] = alive4(state, x, y, z, w);
+          }
+        }
+      }
+    }
+    memcpy(state, new_state, sizeof(state));
+  }
+
+  int active_count = 0;
+  for (int x = 1; x < SIZE - 1; ++x) {
+    for (int y = 1; y < SIZE - 1; ++y) {
+      for (int z = 1; z < SIZE - 1; ++z) {
+        for (int w = 1; w < SIZE - 1; ++w) {
+          active_count += state[x][y][z][w];
+        }
+      }
+    }
+  }
+  return active_count;
+}
+
+int main(int argc, char *argv[]) {
+  if (argc < 2) {
+    printf("Usage: %s <input file>\n", argv[0]);
+    return 0;
+  }
+
+  FILE *fp = fopen(argv[1], "r");
+  if (fp == NULL) {
+    printf("Could not open file %s\n", argv[1]);
+    return 1;
+  }
+
+  bool input[INPUT_SIZE][INPUT_SIZE] = {false};
+  int i = 0;
+  int j = 0;
+  char c;
+  while ((c = fgetc(fp)) != EOF) {
+    if (c == '\n') {
+      i++;
+      j = 0;
+    } else {
+      input[i][j] = (c == '#');
+      j++;
+    }
+  }
+  fclose(fp);
+
+  printf("%d\n", part1(input));
+  printf("%d\n", part2(input));
+
+  return 0;
+}