day4

Makefile

@@ -1,12 +1,14 @@
 all: $(patsubst %.cpp,%.elf,$(wildcard example/*.cpp))
 
+OPT = -Og
+
 include dreamcast/base.mk
 include dreamcast/common.mk
 include dreamcast/headers.mk
 
-MAKEFILE_PATH := $(abspath $(firstword $(MAKEFILE_LIST)))
+MAKEFILE_PATH := $(patsubst %/,%,$(dir $(abspath $(firstword $(MAKEFILE_LIST)))))
-CFLAGS += -I$(dir $(MAKEFILE_PATH))
+CFLAGS += -I$(MAKEFILE_PATH)
-CFLAGS += -I$(dir $(MAKEFILE_PATH))dreamcast/
+CFLAGS += -I$(MAKEFILE_PATH)/dreamcast/
-LIB ?= $(dir $(MAKEFILE_PATH))dreamcast
+LIB ?= $(MAKEFILE_PATH)/dreamcast
 
 include aoc.mk

day2/solution.c

@@ -28,6 +28,14 @@ static int parse_input(const char * input, int length, struct report * report)
   return i;
 }
 
+static int int_sign(int n)
+{
+  if (n < 0)
+    return -1;
+  else
+    return 1;
+}
+
 static bool report_safe(struct report * report, int skip)
 {
   int last_sign = 0;
@@ -45,7 +53,7 @@ static bool report_safe(struct report * report, int skip)
     if (abs(rate) < 1 || abs(rate) > 3)
       return false; // unsafe
 
-    int sign = rate / abs(rate);
+    int sign = int_sign(sign);
     if (last_sign != 0 && sign != last_sign)
       return false; // unsafe
 

day4/input.txt

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+SAXSASMASAMMSAXMMSAMMMAXMAMXMXMSXSASXSMMMAMXSAXAMMMMMMMAMSAAXAMXMMAMAXAMSSXMMSMMMMSSSSSXMXMSXMASMSSMMSMMMSXSASXMSSXMAAXMASAAXSAMXMXSXMXAAMAM
+SMMSAMXAMSSXMMMSAMXSAAAMMSAXMAXAMMAMAAAXSAMXMAMASAAAXAMSAMXMMAMMSXAMMMAMASAMAAAASAMAAAAAXMAMAAASAMXXAAAAAMMMXMXMAXASXSMSXMSSMMXMSAMXXSMSMSAA
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day4/input.txt.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern uint32_t _binary_day4_input_txt_start __asm("_binary_day4_input_txt_start");
+extern uint32_t _binary_day4_input_txt_end __asm("_binary_day4_input_txt_end");
+extern uint32_t _binary_day4_input_txt_size __asm("_binary_day4_input_txt_size");
+
+#ifdef __cplusplus
+}
+#endif

day4/sample1.txt

@@ -0,0 +1,10 @@
+MMMSXXMASM
+MSAMXMSMSA
+AMXSXMAAMM
+MSAMASMSMX
+XMASAMXAMM
+XXAMMXXAMA
+SMSMSASXSS
+SAXAMASAAA
+MAMMMXMMMM
+MXMXAXMASX

day4/sample1.txt.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern uint32_t _binary_day4_sample1_txt_start __asm("_binary_day4_sample1_txt_start");
+extern uint32_t _binary_day4_sample1_txt_end __asm("_binary_day4_sample1_txt_end");
+extern uint32_t _binary_day4_sample1_txt_size __asm("_binary_day4_sample1_txt_size");
+
+#ifdef __cplusplus
+}
+#endif

day4/solution.c

@@ -0,0 +1,217 @@
+#include <stdbool.h>
+
+#include "printf.h"
+
+static int parse_stride(char * input, int length)
+{
+  for (int i = 0; i < length; i++) {
+    if (input[i] == '\n') {
+      return i + 1;
+    }
+  }
+  return -1;
+}
+
+static int parse_height(char * input, int length)
+{
+  int rows = 0;
+  int i;
+  for (i = 0; i < length; i++) {
+    if (input[i] == '\n') {
+      rows += 1;
+    }
+  }
+  if (input[i-1] != '\n') {
+    rows += 1;
+  }
+  return rows;
+}
+
+enum offset_type {
+  N,
+  S,
+  E,
+  W,
+  NE,
+  NW,
+  SE,
+  SW,
+};
+
+static char offsets[][2] = {
+  [N ] = { 0, -1},
+  [S ] = { 0,  1},
+  [E ] = { 1,  0},
+  [W ] = {-1,  0},
+  [NE] = { 1, -1},
+  [NW] = {-1, -1},
+  [SW] = {-1,  1},
+  [SE] = { 1,  1},
+};
+
+static bool xy_inside(int width, int height,
+                      int x, int y)
+{
+  if (y < 0 || x < 0)
+    return false;
+  if (x >= width)
+    return false;
+  if (y >= height)
+    return false;
+  return true;
+}
+
+static char get_char(char * input,
+                     int stride,
+                     int x, int y)
+{
+  int ix = y * stride + x;
+  return input[ix];
+}
+
+static bool offset_match(char * input,
+                         int stride,
+                         int width, int height,
+                         int x, int y,
+                         char * offset,
+                         const char * str,
+                         int str_length)
+{
+  for (int i = 0; i < str_length; i++) {
+    if (!xy_inside(width, height, x, y))
+      return false;
+
+    char c = get_char(input, stride, x, y);
+    if (c != str[i])
+      return false;
+
+    x += offset[0];
+    y += offset[1];
+  }
+
+  return true;
+}
+
+static bool offset_match_centered(char * input,
+                                  int stride,
+                                  int width, int height,
+                                  int x, int y,
+                                  char * offset,
+                                  const char * str,
+                                  int str_length)
+{
+  // blindly assumes odd-numbered str_length
+  // distance from the corner to the center
+  int center = str_length / 2; // floor division
+
+  // go to corner
+  x -= offset[0] * center;
+  y -= offset[1] * center;
+
+  return offset_match(input,
+                      stride,
+                      width, height,
+                      x, y,
+                      offset,
+                      str,
+                      str_length);
+}
+
+static bool offset_match_cross(char * input,
+                               int stride,
+                               int width, int height,
+                               int x, int y,
+                               char * offset,
+                               const char * str,
+                               int str_length)
+{
+  bool match0 = offset_match_centered(input,
+                                      stride,
+                                      width, height,
+                                      x, y,
+                                      offset,
+                                      str,
+                                      str_length);
+  if (!match0)
+    return false;
+
+  char cross1[2] = {-offset[0],  offset[1]};
+  char cross2[2] = { offset[0], -offset[1]};
+
+  bool match1 = offset_match_centered(input,
+                                      stride,
+                                      width, height,
+                                      x, y,
+                                      cross1,
+                                      str,
+                                      str_length);
+  bool match2 = offset_match_centered(input,
+                                      stride,
+                                      width, height,
+                                      x, y,
+                                      cross2,
+                                      str,
+                                      str_length);
+  return match1 || match2;
+}
+
+int day4_part1(char * input, int length)
+{
+  int stride = parse_stride(input, length);
+  int height = parse_height(input, length);
+  int width = stride - 1;
+
+  const char * str = "XMAS";
+  int str_length = 4;
+
+  int match_count = 0;
+  for (int y = 0; y < height; y++) {
+    for (int x = 0; x < width; x++) {
+      for (int o = 0; o < 8; o++) {
+        bool match = offset_match(input,
+                                  stride,
+                                  width, height,
+                                  x, y,
+                                  offsets[o],
+                                  str,
+                                  str_length);
+        match_count += (int)match;
+      }
+    }
+  }
+
+  return match_count;
+}
+
+int day4_part2(char * input, int length)
+{
+  int stride = parse_stride(input, length);
+  int height = parse_height(input, length);
+  int width = stride - 1;
+
+  const char * str = "MAS";
+  int str_length = 3;
+
+  int match_count = 0;
+  for (int y = 0; y < height; y++) {
+    for (int x = 0; x < width; x++) {
+      bool match_ne = offset_match_cross(input,
+                                         stride,
+                                         width, height,
+                                         x, y,
+                                         offsets[NE],
+                                         str,
+                                         str_length);
+      bool match_sw = offset_match_cross(input,
+                                         stride,
+                                         width, height,
+                                         x, y,
+                                         offsets[SW],
+                                         str,
+                                         str_length);
+      match_count += (int)(match_ne || match_sw);
+    }
+  }
+
+  return match_count;
+}

input_dreamcast.inc

@@ -5,6 +5,8 @@
 #include "day3/sample1.txt.h"
 #include "day3/sample2.txt.h"
 #include "day3/input.txt.h"
+#include "day4/sample1.txt.h"
+#include "day4/input.txt.h"
 
 static struct start_size sample[][2] = {
   {
@@ -25,6 +27,12 @@ static struct start_size sample[][2] = {
     { (  char *)&_binary_day3_sample2_txt_start,
       (uint32_t)&_binary_day3_sample2_txt_size   },
   },
+  {
+    { (  char *)&_binary_day4_sample1_txt_start,
+      (uint32_t)&_binary_day4_sample1_txt_size   },
+    { (  char *)&_binary_day4_sample1_txt_start,
+      (uint32_t)&_binary_day4_sample1_txt_size   },
+  },
 };
 
 static struct start_size input[] = {
@@ -34,4 +42,6 @@ static struct start_size input[] = {
     (uint32_t)&_binary_day2_input_txt_size   },
   { (  char *)&_binary_day3_input_txt_start,
     (uint32_t)&_binary_day3_input_txt_size   },
+  { (  char *)&_binary_day4_input_txt_start,
+    (uint32_t)&_binary_day4_input_txt_size   },
 };

runner.inc

@@ -4,9 +4,12 @@ int day2_part1(char * input, int length);
 int day2_part2(char * input, int length);
 int day3_part1(char * input, int length);
 int day3_part2(char * input, int length);
+int day4_part1(char * input, int length);
+int day4_part2(char * input, int length);
 
 part_func solution[][2] = {
   {day1_part1, day1_part2},
   {day2_part1, day2_part2},
   {day3_part1, day3_part2},
+  {day4_part1, day4_part2},
 };

runner_dreamcast.cpp

@@ -278,6 +278,6 @@ int main()
     transfer_scene(font, glyphs);
   }
 
-  while (1);
+  //while (1);
   serial::string("return\n");
 }

solutions.mk

@@ -8,4 +8,7 @@ DAY_OBJ = \
 	day3/sample1.txt.o \
 	day3/sample2.txt.o \
 	day3/input.txt.o \
-	day3/solution.o
+	day3/solution.o \
+	day4/sample1.txt.o \
+	day4/input.txt.o \
+	day4/solution.o