Change C programs to accept input from STDIN

c/2015/1/problem.c

@@ -1,26 +1,31 @@
 #include <stdio.h>
 
+#include "../../lib/aoc.h"
+
 int main() {
-  FILE* input = fopen("../data/2015/1/input.txt", "r");
-  char c;
+  char *input = aoc_read_input();
   int floor = 0;
-  while (fread(&c, 1, 1, input) > 0) {
-    if (c == '(') floor++;
-    else if(c == ')') floor--;
+  int index = 0;
+  while (input[index] > 0) {
+    if (input[index] == '(') floor++;
+    else if(input[index] == ')') floor--;
+    index++;
   }
 
   printf("Part 1: %d\n", floor);
 
   floor = 0;
   int steps = 0;
-  rewind(input);
+  index = 0;
 
-  while (fread(&c, 1, 1, input) > 0) {
-    if (c == '(') floor++;
-    else if(c == ')') floor--;
+  while (input[index] > 0) {
+    if (input[index] == '(') floor++;
+    else if(input[index] == ')') floor--;
     steps++;
     if (floor < 0) break;
+    index++;
   }
 
   printf("Part 2: %d\n", steps);
+  free(input);
 }

c/2015/2/problem.c

@@ -0,0 +1,48 @@
+#include <stdio.h>
+#include <string.h>
+
+#include "../../lib/aoc.h"
+
+int volume(int length, int width, int height) {
+  return length * width * height;
+}
+
+int ribbon_length(int length, int width, int height) {
+  int first_perimeter = (length + width) * 2;
+  int second_perimeter = (length + height) * 2;
+  int third_perimeter = (height + width) * 2;
+  int smallest_perimeter = first_perimeter;
+  if (second_perimeter < smallest_perimeter) smallest_perimeter = second_perimeter;
+  if (third_perimeter < smallest_perimeter) smallest_perimeter = third_perimeter;
+  return smallest_perimeter + volume(length, width, height);
+}
+
+int surface_area(int length, int width, int height) {
+  int first_side = length * width * 2;
+  int second_side = length * height * 2;
+  int third_side = height * width * 2;
+  int smallest_side = first_side;
+  if (second_side < smallest_side) smallest_side = second_side;
+  if (third_side < smallest_side) smallest_side = third_side;
+  return first_side + second_side + third_side + (smallest_side / 2);
+}
+
+int main() {
+  char *input = aoc_read_input();
+  int paper = 0;
+  int ribbon = 0;
+  char *tok = strtok(input, "x");
+  while (tok != NULL) {
+    int l = atoi(tok);
+    tok = strtok(NULL, "x");
+    int w = atoi(tok);
+    tok = strtok(NULL, "\n");
+    int h = atoi(tok);
+    paper += surface_area(l, w, h);
+    ribbon += ribbon_length(l, w, h);
+    tok = strtok(NULL, "x");
+  }
+  printf("Part 1: %d\n", paper);
+  printf("Part 1: %d\n", ribbon);
+  free(input);
+}

c/2015/3/problem.c

@@ -0,0 +1,72 @@
+#include <stdio.h>
+#include <string.h>
+
+#include "../../lib/aoc.h"
+
+int compare(const void *a, const void *b) {
+  return *(int*)a - *(int*)b;
+}
+
+int visited_houses(char *input, int num_santas) {
+  int moves_count = strlen(input);
+  int *positions = calloc(moves_count + 1, sizeof(int)); // +1 for the starting position
+  int **santa_positions = calloc(num_santas, sizeof(int*));
+  for (int i = 0; i < num_santas; i++) {
+    santa_positions[i] = calloc(2, sizeof(int));
+    santa_positions[i][0] = 0;
+    santa_positions[i][1] = 0;
+  }
+  int santa_index = 0;
+  int *santa_position = santa_positions[0];
+
+  positions[0] = 0;
+  int index = 0;
+
+  while (input[index] > 10) {
+    switch(input[index++]) {
+    case '^':
+      santa_position[1] += 1;
+      break;
+    case 'v':
+      santa_position[1] -= 1;
+      break;
+    case '>':
+      santa_position[0] += 1;
+      break;
+    case '<':
+      santa_position[0] -= 1;
+      break;
+    }
+
+    positions[index] = (santa_position[0] * moves_count) + santa_position[1];
+    santa_index = (santa_index + 1) % num_santas;
+    santa_position = santa_positions[santa_index];
+  }
+
+  qsort(positions, moves_count, sizeof(int), compare);
+  int last_position = positions[0];
+  int num_visited_houses = 0;
+
+  for (int i = 0; i < moves_count + 1; i++) {
+    if (positions[i] != last_position) {
+      num_visited_houses++;
+      last_position = positions[i];
+    }
+  }
+
+  free(positions);
+  for (int i = 0; i < num_santas; i++) {
+    free(santa_positions[i]);
+  }
+  free(santa_positions);
+  return num_visited_houses;
+}
+
+int main() {
+  char *input = aoc_read_input();
+
+  printf("Part 1: %d\n", visited_houses(input, 1));
+  printf("Part 2: %d\n", visited_houses(input, 2));
+
+  free(input);
+}

c/2017/1/problem.c

@@ -1,43 +1,35 @@
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
+
+#include "../../lib/aoc.h"
 
 int main() {
-  FILE* input = fopen("../data/2017/1/input.txt", "r");
-  char c1, c2, first_char;
-  long total;
+  char *input = aoc_read_input();
+  int length = strlen(input) - 1;
+  int sum = 0;
 
-  fread(&first_char, 1, 1, input);
-  c2 = first_char;
-
-  while (fread(&c1, 1, 1, input) > 0 && c1 != '\n') {
-    if (c1 == c2) {
-      total += c1 - '0';
-    }
-    c2 = c1;
-  }
-
-  if (c2 == first_char) {
-    total += c2 - '0';
-  }
-
-  printf("Part 1: %d\n", total);
-
-  int num_chars = ftell(input);
-  rewind(input);
-  total = 0;
-
-  char *buffer = malloc(num_chars);
-  fread(buffer, 1, num_chars, input);
-
-  for(int i = 0; i < num_chars / 2; i++) {
-    c1 = buffer[i];
-    c2 = buffer[i + (num_chars / 2)];
-    if (c1 == c2) {
-      total += c1 - '0';
+  for (int i = 0; i < length - 1; i++) {
+    if (input[i] == input[i + 1]) {
+      sum += input[i] - '0';
     }
   }
 
-  total <<= 1;
+  if (input[0] == input[length - 1]) {
+    sum += input[0] - '0';
+  }
 
-  printf("Part 2: %d\n", total);
+  printf("Part 1: %d\n", sum);
+
+  sum = 0;
+
+  for (int i = 0; i < length; i++) {
+    if (input[i] == input[(i + (length / 2)) % length]) {
+      sum += input[i] - '0';
+    }
+  }
+
+  printf("Part 2: %d\n", sum);
+
+  free(input);
 }

c/2017/2/problem.c

@@ -0,0 +1,79 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <limits.h>
+
+#include "../../lib/aoc.h"
+
+int line_checksum_1(char *line) {
+  char **saveptr = malloc(sizeof(char*));
+  char *token = strtok_r(line, "\t", saveptr);
+
+  int min = INT_MAX;
+  int max = INT_MIN;
+
+  while (token != NULL) {
+    int value = atoi(token);
+    if (value < min) min = value;
+    if (value > max) max = value;
+    token = strtok_r(NULL, "\t", saveptr);
+  }
+
+  free(saveptr);
+  return max - min;
+}
+
+int line_checksum_2(char *line) {
+  int tokens[20];
+
+  char **saveptr = malloc(sizeof(char*));
+  char *token = strtok_r(line, "\t", saveptr);
+  int index = 0;
+
+  while (token != NULL) {
+    tokens[index++] = atoi(token);
+    token = strtok_r(NULL, "\t", saveptr);
+  }
+
+  for (int i = 0; i < index; i++) {
+    for (int j = 0; j < index; j++) {
+      if (tokens[i] != tokens[j] && (tokens[i] % tokens[j] == 0)) {
+	free(saveptr);
+	return tokens[i] / tokens[j];
+      }
+    }
+  }
+
+  for (int i = 0; i < index; i++) {
+    printf("%d ", tokens[i]);
+  }
+  printf("ERROR! No checksum found\n");
+
+  return 0;
+}
+
+int main() {
+  char *input = aoc_read_input();
+
+  char **line_saveptr = malloc(sizeof(char*));
+  char *line = strtok_r(input, "\n", line_saveptr);
+
+  int checksum_sum_1 = 0;
+  int checksum_sum_2 = 0;
+
+  while (line != NULL) {
+    char *line_copy = malloc(strlen(line) + 1);
+    strcpy(line_copy, line);
+    checksum_sum_1 += line_checksum_1(line);
+    checksum_sum_2 += line_checksum_2(line_copy);
+    line = strtok_r(NULL, "\n", line_saveptr);
+    free(line_copy);
+  }
+
+  printf("Part 1: %d\n", checksum_sum_1);
+  printf("Part 2: %d\n", checksum_sum_2);
+
+  free(line_saveptr);
+  free(line);
+  free(input);
+}

c/bin/run

@@ -3,4 +3,5 @@
 year=$1
 day=$2
 
-gcc -o $year/$day/problem $year/$day/problem.c && time ./$year/$day/problem
+gcc -o $year/$day/problem $year/$day/problem.c
+time (cat ../data/$year/$day/input.txt | ./$year/$day/problem)

c/lib/aoc.h

@@ -0,0 +1,22 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#define INITIAL_BUFFER_SIZE 2
+
+char *aoc_read_input(void) {
+  int buffer_size = INITIAL_BUFFER_SIZE;
+  char *input_buffer = malloc(buffer_size);
+  int chars_read = read(STDIN_FILENO, input_buffer, buffer_size);
+  char *buffer_position = &input_buffer[chars_read];
+
+  while (chars_read == buffer_size) {
+    buffer_size *= 2;
+    input_buffer = realloc(input_buffer, buffer_size);
+    buffer_position = &input_buffer[chars_read];
+    chars_read += read(STDIN_FILENO, buffer_position, buffer_size / 2);
+  }
+
+  input_buffer[chars_read] = 0;
+  return input_buffer;
+}