Initial commit

2020/day14/day14.c

@@ -0,0 +1,123 @@
+#include "uthash.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+struct memcell {
+  unsigned long key;
+  unsigned long val;
+  UT_hash_handle hh;
+};
+
+unsigned long part1(FILE *fp) {
+  char *buf = NULL;
+  size_t buf_size = 0;
+  struct memcell *mem = NULL;
+  char mask[36];
+
+  while (getline(&buf, &buf_size, fp) != -1) {
+    if (strncmp(buf, "mask", 4) == 0) {
+      sscanf(buf, "mask = %s", mask);
+    }
+
+    else {
+      unsigned long addr, val;
+      sscanf(buf, "mem[%ld] = %ld", &addr, &val);
+
+      for (int i = 0; i < 36; ++i) {
+        if (mask[35 - i] == '1') {
+          val |= 1UL << i;
+        } else if (mask[35 - i] == '0') {
+          val &= ~(1UL << i);
+        }
+      }
+
+      struct memcell *elt = (struct memcell *)malloc(sizeof(struct memcell));
+      struct memcell *prev_elt =
+          (struct memcell *)malloc(sizeof(struct memcell));
+      elt->key = addr;
+      elt->val = val;
+      HASH_REPLACE(hh, mem, key, sizeof(unsigned long), elt, prev_elt);
+    }
+  }
+
+  unsigned long sum = 0;
+  for (struct memcell *cell = mem; cell != NULL; cell = cell->hh.next) {
+    sum += cell->val;
+  }
+
+  return sum;
+}
+
+unsigned long part2(FILE *fp) {
+  char *buf = NULL;
+  size_t buf_size = 0;
+  struct memcell *mem = NULL;
+  char mask[36];
+  int xcount;
+
+  while (getline(&buf, &buf_size, fp) != -1) {
+    if (strncmp(buf, "mask", 4) == 0) {
+      sscanf(buf, "mask = %s", mask);
+      xcount = 0;
+      for (int i = 0; i < 36; ++i) {
+        if (mask[i] == 'X') {
+          xcount++;
+        }
+      }
+    }
+
+    else {
+      unsigned long addr, val;
+      sscanf(buf, "mem[%ld] = %ld", &addr, &val);
+
+      for (unsigned long m = 0; m < (1UL << xcount); ++m) {
+        unsigned long new_addr = addr;
+        int x_idx = 0;
+        for (int i = 0; i < 36; ++i) {
+          if (mask[35 - i] == '1') {
+            new_addr |= 1UL << i;
+          } else if (mask[35 - i] == 'X') {
+            unsigned long bit = (1UL & (m >> x_idx));
+            new_addr ^= (-bit ^ new_addr) & (1UL << i);
+            x_idx++;
+          }
+        }
+
+        struct memcell *elt = (struct memcell *)malloc(sizeof(struct memcell));
+        struct memcell *prev_elt =
+            (struct memcell *)malloc(sizeof(struct memcell));
+        elt->key = new_addr;
+        elt->val = val;
+        HASH_REPLACE(hh, mem, key, sizeof(unsigned long), elt, prev_elt);
+      }
+    }
+  }
+
+  unsigned long sum = 0;
+  for (struct memcell *cell = mem; cell != NULL; cell = cell->hh.next) {
+    sum += cell->val;
+  }
+
+  return sum;
+}
+
+int main(int argc, char *argv[]) {
+  if (argc < 2) {
+    printf("Usage: %s <input file>\n", argv[0]);
+    return 0;
+  }
+
+  FILE *fp = fopen(argv[1], "r");
+  if (fp == NULL) {
+    printf("Could not open file %s\n", argv[1]);
+    return 1;
+  }
+
+  printf("%lu\n", part1(fp));
+  rewind(fp);
+  printf("%lu\n", part2(fp));
+  fclose(fp);
+
+  return 0;
+}