Day 18. I thought this was supposed to be hard?

1 files changed, 113 insertions, 0 deletions

diff --git a/day18/day18.c b/day18/day18.c
new file mode 100644
index 0000000..180cd1e
--- /dev/null
+++ b/day18/day18.c
@@ -0,0 +1,113 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#define ROWS 100
+#define COLS 100
+
+void new(int*** a) {
+  int i;
+  *a = (int**) malloc(ROWS * sizeof(int*));
+  for(i=0; i<ROWS; i++)
+    (*a)[i] = (int*) malloc(COLS * sizeof(int));
+}
+
+void delete(int** a) {
+  int i;
+  for(i=0; i<ROWS; i++)
+    free(a[i]);
+  free(a);
+}
+
+void copy(int** src, int** dst) {
+  int i, j;
+  for(i=0; i<ROWS; i++)
+    for(j=0; j<COLS; j++)
+      dst[i][j] = src[i][j];
+}
+
+void readinto(int** a) {
+  int i, j, ch;
+  for(i=0; i<ROWS; i++) {
+    for(j=0; j<COLS; j++) {
+      ch = getchar();
+      switch(ch) {
+        case '.': a[i][j] = 0; break;
+        case '#': a[i][j] = 1;
+      }
+    }
+    getchar(); // '\n'
+  }
+}
+
+int ncount(int** a, int r, int c) {
+  int n = 0, i, j;
+
+  for(i=-1; i<2; i++)
+    for(j=-1; j<2; j++)
+      if((r+i)>=0 && (r+i)<ROWS && (c+j)>=0 && (c+j)<COLS && !(i == 0 && j == 0))
+        n += a[r+i][c+j];
+
+  return n;
+}
+
+void step(int** old, int** new) {
+  int i, j, c;
+
+  for(i=0; i<ROWS; i++)
+    for(j=0; j<COLS; j++) {
+      c = ncount(old, i, j);
+      if(old[i][j]) {
+        if(c == 2 || c == 3) new[i][j] = 1;
+        else                 new[i][j] = 0;
+      } else {
+        if(c == 3) new[i][j] = 1;
+        else       new[i][j] = 0;
+      }
+    }
+}
+
+void corners(int** a) {
+  a[0][0] = a[ROWS-1][0] = a[0][COLS-1] = a[ROWS-1][COLS-1] = 1;
+}
+
+int numlights(int** a) {
+  int n = 0, i, j;
+
+  for(i=0; i<ROWS; i++)
+    for(j=0; j<COLS; j++)
+      n += a[i][j];
+
+  return n;
+}
+
+int main() {
+  int i, **input, **this, **that;
+
+  new(&input);
+  new(&this);
+  new(&that);
+
+  readinto(input);
+
+  copy(input, this);
+  for(i=0; i<50; i++) {
+    step(this, that);
+    step(that, this);
+  }
+  printf("Number of lights: %d\n", numlights(this));
+
+  copy(input, this);
+  corners(this);
+  for(i=0; i<50; i++) {
+    step(this, that);
+    corners(that);
+    step(that, this);
+    corners(this);
+  }
+  printf("Number of lights: %d\n", numlights(this));
+
+  delete(input);
+  delete(this);
+  delete(that);
+  return 0;
+}