day2

abs.h

@@ -0,0 +1,9 @@
+#pragma once
+
+static inline int abs(int n)
+{
+  if (n < 0)
+    return -n;
+  else
+    return n;
+}

aoc.mk

@@ -21,5 +21,14 @@ DAY1_OBJ = \
 	day1/input.txt.o \
 	day1/solution.o
 
+DAY2_OBJ = \
+	day2/sample1.txt.o \
+	day2/input.txt.o \
+	day2/solution.o
+
+DAY_OBJ = \
+	$(DAY1_OBJ) \
+	$(DAY2_OBJ)
+
 aoc.elf: LDSCRIPT = $(LIB)/main.lds
-aoc.elf: $(START_OBJ) $(OBJ) $(DREAMCAST_OBJ) $(DAY1_OBJ)
+aoc.elf: $(START_OBJ) $(OBJ) $(DREAMCAST_OBJ) $(DAY_OBJ)

day1/solution.c

@@ -1,13 +1,13 @@
-#include "input.h"
 #include "parse.h"
 #include "heapsort.h"
+#include "abs.h"
 
 struct list {
   int left[1000];
   int right[1000];
 };
 
-int parse_input(const char * input, int length, struct list * list)
+static int parse_input(const char * input, int length, struct list * list)
 {
   const char * end = input + length;
 
@@ -23,14 +23,6 @@ int parse_input(const char * input, int length, struct list * list)
   return i;
 }
 
-int abs(int n)
-{
-  if (n < 0)
-    return -n;
-  else
-    return n;
-}
-
 int day1_part1(char * input, int length)
 {
   struct list list;

day2/input.txt.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern uint32_t _binary_day2_input_txt_start __asm("_binary_day2_input_txt_start");
+extern uint32_t _binary_day2_input_txt_end __asm("_binary_day2_input_txt_end");
+extern uint32_t _binary_day2_input_txt_size __asm("_binary_day2_input_txt_size");
+
+#ifdef __cplusplus
+}
+#endif

day2/sample1.txt

@@ -0,0 +1,6 @@
+7 6 4 2 1
+1 2 7 8 9
+9 7 6 2 1
+1 3 2 4 5
+8 6 4 4 1
+1 3 6 7 9

day2/sample1.txt.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern uint32_t _binary_day2_sample1_txt_start __asm("_binary_day2_sample1_txt_start");
+extern uint32_t _binary_day2_sample1_txt_end __asm("_binary_day2_sample1_txt_end");
+extern uint32_t _binary_day2_sample1_txt_size __asm("_binary_day2_sample1_txt_size");
+
+#ifdef __cplusplus
+}
+#endif

day2/solution.c

@@ -0,0 +1,90 @@
+#include <stdbool.h>
+
+#include "parse.h"
+#include "printf.h"
+#include "abs.h"
+
+struct report {
+  int level[16];
+  int length;
+};
+
+static int parse_input(const char * input, int length, struct report * report)
+{
+  const char * end = input + length;
+
+  int i = 0;
+  while (input < end) {
+    report[i].length = 0;
+    while (true) {
+      input = parse_base10(input, &report[i].level[report[i].length++]);
+      if (*input != ' ')
+        break;
+      input = parse_skip(input, ' ');
+    }
+    input = parse_skip(input, '\n');
+    i++;
+  }
+  return i;
+}
+
+static bool report_safe(struct report * report, int skip)
+{
+  int last_sign = 0;
+  int i = (skip == 0) ? 1 : 0;
+  int last = report->level[i];
+
+  for (++i; i < report->length; i++) {
+    if (i == skip)
+      continue;
+
+    int cur = report->level[i];
+
+    int rate = last - cur;
+
+    if (abs(rate) < 1 || abs(rate) > 3)
+      return false; // unsafe
+
+    int sign = rate / abs(rate);
+    if (last_sign != 0 && sign != last_sign)
+      return false; // unsafe
+
+    last_sign = sign;
+    last = cur;
+  }
+
+  return true;
+}
+
+int day2_part1(char * input, int length)
+{
+  struct report report[1000];
+
+  int report_count = parse_input(input, length, report);
+
+  int sum = 0;
+  for (int i = 0; i < report_count; i++) {
+    sum += (int)report_safe(&report[i], -1);
+  }
+
+  return sum;
+}
+
+int day2_part2(char * input, int length)
+{
+  struct report report[1000];
+
+  int report_count = parse_input(input, length, report);
+
+  int sum = 0;
+  for (int i = 0; i < report_count; i++) {
+    for (int j = -1; j < report[i].length; j++) {
+      bool safe = report_safe(&report[i], j);
+      sum += (bool)safe;
+      if (safe)
+        break;
+    }
+  }
+
+  return sum;
+}

input_dreamcast.c

@@ -6,6 +6,9 @@
 #include "day1/sample1.txt.h"
 #include "day1/input.txt.h"
 
+#include "day2/sample1.txt.h"
+#include "day2/input.txt.h"
+
 struct start_size {
   char * start;
   uint32_t size;
@@ -14,6 +17,9 @@ struct start_size {
 static struct start_size input[] = {
   { (  char *)&_binary_day1_input_txt_start,
     (uint32_t)&_binary_day1_input_txt_size   },
+
+  { (  char *)&_binary_day2_input_txt_start,
+    (uint32_t)&_binary_day2_input_txt_size   },
 };
 
 static struct start_size sample[][2] = {
@@ -23,6 +29,12 @@ static struct start_size sample[][2] = {
     { (  char *)&_binary_day1_sample1_txt_start,
       (uint32_t)&_binary_day1_sample1_txt_size   },
   },
+  {
+    { (  char *)&_binary_day2_sample1_txt_start,
+      (uint32_t)&_binary_day2_sample1_txt_size   },
+    { (  char *)&_binary_day2_sample1_txt_start,
+      (uint32_t)&_binary_day2_sample1_txt_size   },
+  },
 };
 
 const int input_size = (sizeof (input)) / (sizeof (input[0]));

runner.c

@@ -1,14 +1,19 @@
+#include <stdbool.h>
+
 #include "printf.h"
 #include "input.h"
 #include "runner.h"
 
 int day1_part1(char * input, int length);
 int day1_part2(char * input, int length);
+int day2_part1(char * input, int length);
+int day2_part2(char * input, int length);
 
 typedef int (* part_func)(char * input, int length);
 
 part_func solution[][2] = {
   {day1_part1, day1_part2},
+  {day2_part1, day2_part2},
 };
 const int solution_days = (sizeof (solution)) / (sizeof (solution[0]));