Day two

day-02-c/.gitignore

@@ -0,0 +1 @@
+*.out

day-02-c/task1.c

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+#include <stdio.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <limits.h>
+
+
+int main(int argc, char** argv) {
+	if (argc != 2) {
+		fputs("Usage: ", stdout);
+		fputs(argv[0], stdout);
+		fputs(" <input file>\n", stdout);
+		return 1;
+	}
+
+	FILE* file = fopen(argv[1], "r");
+
+	unsigned int safe_count = 0;
+
+	const int max_length = 16;
+	char buffer[17];
+	int buf_length = 0;
+
+	int line_no = 0;
+	while (true) {
+		bool first_number = true;
+		int last_number = INT_MIN;
+		int last_delta = 0;
+		bool safe = true;
+		int c;
+		while (true) {
+			c = fgetc(file);
+			if (buf_length < max_length && c >= '0' && c <= '9') {
+				buffer[buf_length] = c;
+				buf_length++;
+				continue;
+			}
+
+			if (buf_length > 0) {
+				buffer[buf_length] = 0;
+				int number = atoi(buffer);
+
+				if (first_number) {
+					first_number = false;
+				} else {
+					int delta = number - last_number;
+					if (last_delta != 0 && delta * last_delta < 0) {
+						safe = false;
+					} else if (delta == 0 || abs(delta) > 3) {
+						safe = false;
+					}
+					last_delta = delta;
+				}
+
+				last_number = number;
+				buf_length = 0;
+			}
+			
+			if (c == EOF || c == '\n') {
+				break;
+			}
+		}
+
+		if (safe && !first_number) {
+			safe_count++;
+		}
+		line_no++;
+
+		if (c == EOF) {
+			break;
+		}
+	}
+
+	printf("Safe count: %d\n", safe_count);
+
+	fclose(file);
+}

day-02-c/task2.c

@@ -0,0 +1,120 @@
+#include <stdio.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+
+
+void print_numbers(int* numbers, int numbers_length);
+bool are_safe(int* numbers, int numbers_length);
+int find_first_unsafe(int* numbers, int numbers_length);
+
+const int MAX_NUMBER_LENGTH = 16;
+const int MAX_NUMBERS = 100;
+
+int main(int argc, char** argv) {
+	if (argc != 2) {
+		fputs("Usage: ", stdout);
+		fputs(argv[0], stdout);
+		fputs(" <input file>\n", stdout);
+		return 1;
+	}
+
+	FILE* file = fopen(argv[1], "r");
+
+	unsigned int safe_count = 0;
+
+	int line_no = 0;
+	while (true) {
+		char buffer[MAX_NUMBER_LENGTH];
+		int buf_length = 0;
+		int numbers[MAX_NUMBERS];
+		int numbers_length = 0;
+		int c;
+
+		while (true) {
+			c = fgetc(file);
+			if (buf_length < MAX_NUMBER_LENGTH && c >= '0' && c <= '9') {
+				buffer[buf_length++] = c;
+				continue;
+			}
+
+			if (buf_length > 0 && numbers_length < MAX_NUMBERS) {
+				buffer[buf_length] = 0;
+				int number = atoi(buffer);
+				numbers[numbers_length++] = number;
+				buf_length = 0;
+			}
+			
+			if (c == EOF || c == '\n') {
+				break;
+			}
+		}
+
+		if (numbers_length > 0 && are_safe(numbers, numbers_length)) {
+			safe_count++;
+		}
+
+		line_no++;
+
+		if (c == EOF) {
+			break;
+		}
+	}
+
+	printf("Safe count: %d\n", safe_count);
+
+	fclose(file);
+}
+
+bool are_safe(int* numbers, int numbers_length) {
+	print_numbers(numbers, numbers_length);
+
+	int first_unsafe = find_first_unsafe(numbers, numbers_length);
+	if (first_unsafe < 0) {
+		return true;
+	}
+
+	int without[MAX_NUMBERS];
+	memcpy(without, numbers, sizeof(int) * first_unsafe);
+	memcpy(without + first_unsafe, numbers + first_unsafe + 1, sizeof(int) * (numbers_length - 1));
+
+	if (find_first_unsafe(without, numbers_length - 1) < 0) {
+		return true;
+	}
+	without[first_unsafe] = numbers[first_unsafe];
+
+	return find_first_unsafe(without, numbers_length - 1) < 0;
+}
+
+int find_first_unsafe(int* numbers, int numbers_length) {
+	if (numbers_length <= 1) {
+		return -1;
+	}
+
+	int last_number = numbers[1];
+	int last_delta = last_number - numbers[0];
+	
+	if (last_delta == 0 || abs(last_delta) > 3) {
+		return 0;
+	}
+
+	for (int i = 2; i < numbers_length; i++) {
+		int number = numbers[i];
+		int delta = number - last_number;
+		if (delta == 0 || abs(delta) > 3) {
+			return i - 1;
+		} else if (delta * last_delta < 0) {
+			return i - 1;
+		}
+		last_number = number;
+		last_delta = delta;
+	}
+	return -1;
+}
+
+void print_numbers(int* numbers, int numbers_length) {
+	for (int i = 0; i < numbers_length; i++) {
+		printf("%d ", numbers[i]);
+	}
+	puts("");
+}