Day 1

.gitignore

@@ -0,0 +1,7 @@
+*.in
+*.out
+compile_commands.json
+.cache/
+
+day_*
+!day_*.c

Makefile

@@ -0,0 +1,9 @@
+CC ?= clang
+CFLAGS = -O0 -g -Wall -Wextra
+
+%.o: %.c
+	$(CC) $(CFLAGS) -c -o $@ $<
+
+day_1: day_1.o
+	$(CC) -o $@ $^
+	./day_1 day_1.in

day_1.c

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+#include "stdio.h"
+#include "stdlib.h"
+#include "string.h"
+
+int compare(const void* a, const void* b) {
+  return (*(int*)a - *(int*)b);
+}
+
+int main(int argc, char* argv[]) {
+  int size = 0;
+  int lines = 0;
+  int sum = 0;
+  int* list1 = NULL;
+  int* list2 = NULL;
+
+  if(argc < 2) {
+    fprintf(stderr, "Filename required\n");
+    return 1;
+  }
+
+  FILE* file = fopen(argv[1], "r");
+  if(file == NULL) {
+    fprintf(stderr, "Could not open %s\n", argv[1]);
+    return 2;
+  }
+
+  char* line = NULL;
+  size_t line_size = 0;
+  while(getline(&line, &line_size, file) > 0) {
+    lines += 1;
+  }
+
+  rewind(file);
+  list1 = malloc(sizeof(int)*lines);
+  list2 = malloc(sizeof(int)*lines);
+
+  for(int i = 0; i < lines; i++) {
+    char* line_save = NULL;
+    getline(&line, &line_size, file);
+    char* num1 = strtok_r(line, " ", &line_save);
+    char* num2 = strtok_r(NULL, " ", &line_save);
+    if(num1 == NULL || num2 == NULL) continue;
+
+    list1[i] = atoi(num1);
+    list2[i] = atoi(num2);
+    size += 1;
+  }
+  free(line);
+
+  qsort(list1, size, sizeof(int), compare);
+  qsort(list2, size, sizeof(int), compare);
+
+  for(int i = 0; i < size; i++) {
+    sum += abs(list1[i] - list2[i]);
+  }
+
+  fprintf(stdout, "Sum: %d\n", sum);
+
+  int similarity = 0;
+  int* counts = malloc(sizeof(int)*size);
+  memset(counts, 0, sizeof(int)*size);
+
+  for(int i = 0; i < size; i++) {
+    for(int j = 0; j < size; j++) {
+      if(list1[i] == list2[j]) counts[i] += 1;
+    }
+  }
+
+  for(int i = 0; i < size; i++){
+    similarity += list1[i] * counts[i];
+  }
+
+  fprintf(stdout, "Similarity: %d\n", similarity);
+
+  return 0;
+}