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