diff --git a/c/lib/aoc.h b/c/lib/aoc.h
index aac3147..1576529 100644
--- a/c/lib/aoc.h
+++ b/c/lib/aoc.h
@@ -2,6 +2,8 @@
 #include <stdio.h>
 #include <unistd.h>
 
+#include "hashmap.h"
+
 #define INITIAL_BUFFER_SIZE 2
 
 char *input_buffer;
diff --git a/c/lib/hashmap.h b/c/lib/hashmap.h
new file mode 100644
index 0000000..1c81d16
--- /dev/null
+++ b/c/lib/hashmap.h
@@ -0,0 +1,44 @@
+#define AOC_HASHMAP_RADIX 1024
+
+int aoc_hash(const char *string) {
+  int len = strlen(string);
+  int hash = 1;
+  for (int i = 0; i < len; i++) {
+    hash *= 7;
+    hash += string[i] * 13;
+    hash %= AOC_HASHMAP_RADIX;
+  }
+
+  return hash;
+}
+
+typedef struct AocHashmapNode AocHashmapNode;
+
+typedef struct AocHashmapNode {
+  char *key;
+  long value;
+  AocHashmapNode *next;
+} AocHashmapNode;
+
+typedef struct AocHashmap {
+  AocHashmapNode* buckets[AOC_HASHMAP_RADIX];
+} AocHashmap;
+
+AocHashmapNode *aoc_hashmap_get(AocHashmap *map, char *key) {
+  int hash = aoc_hash(key);
+  AocHashmapNode *node = map->buckets[hash];
+  while (node != NULL && strcmp(node->key, key) != 0) node = node->next;
+  return node;
+}
+
+void *aoc_hashmap_put(AocHashmap *map, char *key, long value) {
+  int hash = aoc_hash(key);
+  AocHashmapNode *node = map->buckets[hash];
+  while (node != NULL) node = node->next;
+  map->buckets[hash] = malloc(sizeof(AocHashmapNode));
+  node = map->buckets[hash];
+  node->key = malloc(strlen(key) + 1);
+  strcpy(node->key, key);
+  node->value = value;
+  node->next = NULL;
+}