day 1 part 2

day 1/2.c

@@ -0,0 +1,87 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+unsigned int hash_int(unsigned int key) {
+  /* Robert Jenkins' 32 bit Mix Function */
+  key += (key << 12);
+  key ^= (key >> 22);
+  key += (key << 4);
+  key ^= (key >> 9);
+  key += (key << 10);
+  key ^= (key >> 2);
+  key += (key << 7);
+  key ^= (key >> 12);
+
+  /* Knuth's Multiplicative Method */
+  key = (key >> 3) * 2654435761;
+
+  return key;
+}
+
+#define TABLE_SIZE 16384
+#define BUFFER_SIZE 1024
+
+int main(void) {
+  FILE *fp = fopen("input", "r");
+
+  size_t lineCount = 0;
+
+  char buffer[BUFFER_SIZE] = {0};
+
+  // get number of lines
+  size_t read = 0;
+
+  while ((read = fread(&buffer, sizeof(char), BUFFER_SIZE, fp))) {
+    for (size_t i = 0; i < read; i++) {
+      if (buffer[i] == '\n') {
+        lineCount++;
+      }
+    }
+  }
+
+  rewind(fp);
+
+  // get data from file
+  unsigned int *left = malloc((lineCount * 2 + 1) * sizeof(int));
+  // haha pointer arithmetic go brrr
+  unsigned int *right = left + lineCount;
+
+  for (size_t i = 0; i < lineCount; i++) {
+    unsigned int leftNum, rightNum;
+    int numsGot = fscanf(fp, "%u   %u\n", &leftNum, &rightNum);
+
+    if (numsGot == 2) {
+      left[i] = leftNum;
+      right[i] = rightNum;
+    }
+  }
+
+  unsigned int hash_map[TABLE_SIZE] = {0};
+
+  unsigned sum = 0;
+  for (size_t i = 0; i < lineCount; i++) {
+    const unsigned int key = hash_int(left[i]) % TABLE_SIZE;
+
+    if (hash_map[key] == 0) {
+      unsigned int similarity_score = 0;
+      for (size_t j = 0; j < lineCount; j++) {
+        if (left[i] == right[j]) {
+          similarity_score++;
+        }
+      }
+
+      similarity_score *= left[i];
+
+      hash_map[key] = similarity_score;
+    }
+
+    sum += hash_map[key];
+  }
+
+  printf("%d\n", sum);
+
+  free(left);
+  fclose(fp);
+
+  return 0;
+}