Index: aoc2015.c
==================================================================
--- aoc2015.c
+++ aoc2015.c
@@ -1,26 +1,21 @@
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <string.h>
 #include "aocdailies.h"
 #include "aocutils.h"
 
 struct House {
     int row, col;
 };
 
-#ifndef MAX_HOUSES
-#  define MAX_HOUSES 2400
-#else
-#  error MAX_HOUSES already defined
-#endif
 void aoc201503(char *data, size_t len) {
     (void)len; // unused argument
     char *data2 = data; // save it
-    struct House house[MAX_HOUSES] = {0};
-    unsigned nhouse = 1; // house at [0, 0] visited
+    struct House *house = malloc(512 * sizeof *house); // assume it worked
+    unsigned mhouse = 512, nhouse = 1;
+    house[0].row = house[0].col = 0; // house at [0, 0] visited
     int x = 0, y = 0;
     while (*data) {
         switch (*data) {
             default: break;
             case '^': y++; break;
@@ -35,28 +30,33 @@
                 visited = true;
                 break;
             }
         }
         if (!visited) {
-            if (nhouse == MAX_HOUSES) {
-                fprintf(stderr, "Need more houses in aoc201503()\n");
-                exit(EXIT_FAILURE);
+            if (nhouse == mhouse) {
+                // grow the array (by golden ratio)
+                struct House *tmp = realloc(house, (13*mhouse) / 8 * sizeof *house);
+                if (!tmp) {
+                    fprintf(stderr, "no memory. program aborted\n");
+                    exit(EXIT_FAILURE);
+                }
+                house = tmp;
+                mhouse = (13*mhouse) / 8;
             }
             house[nhouse].row = x;
             house[nhouse].col = y;
             nhouse += 1;
         }
     }
     printf("Santa delivered at least 1 present to %u houses.\n", nhouse);
 
-    memset(house, 0, sizeof house);
-    nhouse = 1;
-    struct House p[2] = {0};
-    int who = 1; // 0: santa; 1: santa bot
+    // reuse house array for part 2; don't worry about its contents
+    nhouse = 1; // house at [0, 0] still visited :)
+    struct House p[2] = {0}; // coordinates of santa and bot
+    int who = 0; // 0: santa; 1: santa bot
     // go around from the beginning
     while (*data2) {
-        who = 1 - who; // santa; bot; santa; bot; ..., ..., ...
         switch (*data2) {
             default: break;
             case '^': p[who].row++; break;
             case 'v': p[who].row--; break;
             case '>': p[who].col++; break;
@@ -69,22 +69,28 @@
                 visited = true;
                 break;
             }
         }
         if (!visited) {
-            if (nhouse == MAX_HOUSES) {
-                fprintf(stderr, "Need more houses in aoc201503()\n");
-                exit(EXIT_FAILURE);
+            if (nhouse == mhouse) {
+                // grow the array (by golden ratio)
+                struct House *tmp = realloc(house, (13*mhouse) / 8 * sizeof *house);
+                if (!tmp) {
+                    fprintf(stderr, "no memory. program aborted\n");
+                    exit(EXIT_FAILURE);
+                }
+                house = tmp;
+                mhouse = (13*mhouse) / 8;
             }
             house[nhouse].row = p[who].row;
             house[nhouse].col = p[who].col;
             nhouse += 1;
         }
+        who = 1 - who; // santa; bot; santa; bot; ..., ..., ...
     }
     printf("Santa and santa bot delivered at least 1 present to %u houses.\n", nhouse);
 }
-#undef MAX_HOUSES
 
 void aoc201502(char *data, size_t len) {
     (void)len; // unused argument
     unsigned sqf = 0, f = 0;
     for (;;) {