From 50a873db767f62befc8dc9b7abb96018bdb84d61 Mon Sep 17 00:00:00 2001
From: Nathan Lasseter <Nathan Lasseter nathan@bytemark.co.uk>
Date: Fri, 4 Dec 2015 15:56:07 +0000
Subject: Day 3 *really* needed to be C.

---
 day3.c | 84 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 84 insertions(+)
 create mode 100644 day3.c

diff --git a/day3.c b/day3.c
new file mode 100644
index 0000000..00dca81
--- /dev/null
+++ b/day3.c
@@ -0,0 +1,84 @@
+#include <stdlib.h>
+#include <stdio.h>
+
+int** make2dWithOffset(int rows, int cols, int roff, int coff) {
+  int i;
+
+  int** arr = (int**) malloc(rows * sizeof(int*));
+  for(i = 0; i < rows ; i++)
+    arr[i] = (int*) malloc(cols * sizeof(int)) + coff;
+
+  return (arr + roff);
+}
+
+void free2dWithOffset(int** arr, int rows, int roff) {
+  int i;
+  for(i = -roff; i < rows - roff ; i++)
+    free(arr[i]);
+  free(arr - roff);
+}
+
+int main() {
+  int** somap = make2dWithOffset(400, 400, 200, 200);
+  int** rsmap = make2dWithOffset(400, 400, 200, 200);
+  int ch, i, j, sosum = 0, rssum = 0, odd = 1;
+  int soeasting = 0, sonorthing = 0,
+      seasting = 0, snorthing = 0,
+      rseasting = 0, rsnorthing = 0;
+
+  for(i = -200; i < 200; i++)
+    for(j = -200; j < 200 ; j++) {
+      somap[i][j] = 0;
+      rsmap[i][j] = 0;
+    }
+
+  somap[0][0] = 1;
+  rsmap[0][0] = 2;
+
+  while((ch = getchar()) != EOF) {
+    switch(ch) {
+      case '<':
+        soeasting--;
+        if (odd)
+          seasting--;
+        else
+          rseasting--;
+        break;
+      case '>':
+        soeasting++;
+        if (odd)
+          seasting++;
+        else
+          rseasting++;
+        break;
+      case 'v':
+        sonorthing--;
+        if (odd)
+          snorthing--;
+        else
+          rsnorthing--;
+        break;
+      case '^':
+        sonorthing++;
+        if (odd)
+          snorthing++;
+        else
+          rsnorthing++;
+    }
+    odd = !odd;
+    somap[soeasting][sonorthing]++;
+    rsmap[seasting][snorthing]++;
+    rsmap[rseasting][rsnorthing]++;
+  }
+
+  for(i = -200; i < 200; i++)
+    for(j = -200; j < 200 ; j++) {
+      if(somap[i][j] > 0)
+        sosum++;
+      if(rsmap[i][j] > 0)
+        rssum++;
+    }
+
+  printf("Santa only: %d\nRobosanta:  %d\n", sosum, rssum);
+  return 0;
+}
-- 
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