diff options
Diffstat (limited to '08.c')
| -rw-r--r-- | 08.c | 212 |
1 files changed, 212 insertions, 0 deletions
@@ -0,0 +1,212 @@ +#include <stdlib.h> +#include <stdio.h> +#include <string.h> +#include <err.h> +#include <math.h> +#include "input.h" + +#define INPUT "input/08.txt" + +#define INPUT_DIGIT_SIZE 10 +#define OUTPUT_DIGIT_SIZE 4 + +#define EXPECTED1 504L +#define EXPECTED2 1073431L + +void part1(struct input_str* input) { + long sum = 0; + for(size_t i = 0; i < input->line_count; i++) { + // copy string as strtok will mess with it + int len = strlen(input->lines[i]); + char* line = malloc(len * sizeof(char)); + memset(line, '\0', len); + strncpy(line, input->lines[i], len); + char* output_start = strchr(line, '|'); + char* token = strtok(output_start + 1, " "); + while(token != NULL) { + int token_length = strlen(token); + // respectively digists 1, 4, 7 and 8 + if(token_length == 2 || token_length == 4 || token_length == 3 || token_length == 7) + sum++; + + token = strtok(NULL, " "); + } + //free(line); TODO causes memory corruption + } + + CHECK(sum, EXPECTED1); +} + +int count_segment(int digit) { + int count = 0; + for(int p = 0; p < 10; p++) { + int segment_mask = 1 << p; + if((digit & segment_mask) == segment_mask) + count++; + } + return count; +} + +int parse_digit(char* token) { + // digits are parsed with segments mapped to bits as follows : 0abcdefg + int result = 0; + int p = 0; + while(token[p] != '\0') { + switch(token[p]) { + case 'a': + result |= (1 << 6); + break; + case 'b': + result |= (1 << 5); + break; + case 'c': + result |= (1 << 4); + break; + case 'd': + result |= (1 << 3); + break; + case 'e': + result |= (1 << 2); + break; + case 'f': + result |= (1 << 1); + break; + case 'g': + result |= 1; + break; + default: + err(1, "unexpected token"); + } + p++; + } + return result; +} + +void part2(struct input_str* input) { + long sum = 0; + for(size_t i = 0; i < input->line_count; i++) { + int digits[INPUT_DIGIT_SIZE]; + // copy string as strtok will mess with it + int len = strlen(input->lines[i]); + char* line = malloc(len * sizeof(char)); + memset(line, '\0', len); + strncpy(line, input->lines[i], len); + char* token = strtok(line, " "); + for(int t = 0; t < INPUT_DIGIT_SIZE; t++) { + digits[t] = parse_digit(token); + token = strtok(NULL, " "); + } + + int digits_code[10] = { 0 }; + // first pass to identify 1, 4, 7, 8 + for(int p = 0; p < 10; p++) { + int digit = digits[p]; + int segment_count = count_segment(digit); + if(segment_count == 3) { + digits_code[7] = digit; // this is 7 + digits[p] = 0; + } + else if(segment_count == 4) { + digits_code[4] = digit; // this is 4 + digits[p] = 0; + } + else if(segment_count == 2) { + digits_code[1] = digit; // this is 0 + digits[p] = 0; + } + else if(segment_count == 7) { + digits_code[8] = digit; // this is 8 + digits[p] = 0; + } + } + // second pass identifies 2, 3 and 5 + for(int p = 0; p < 10; p++) { + int digit = digits[p]; + if(digit == 0) + continue; // this digit was identified by previous pass + + int digit_segment_count = count_segment(digit); + if(digit_segment_count == 5) { + if(count_segment(digits[p] & digits_code[7]) == 3) { + digits_code[3] = digit; // this is 3 (5 segments and those of 7) + digits[p] = 0; + } + else if(count_segment(digits[p] & digits_code[4]) == 2) { + digits_code[2] = digit; // this is 2 (5 segments and 2 in common with 4) + digits[p] = 0; + } + else if(count_segment(digits[p] & digits_code[4]) == 3) { + digits_code[5] = digit; // this si 5 (5 segments and 3 in common with 4) + digits[p] = 0; + } + } + } + // third pass identifies 0, 6 and 9 + for(int p = 0; p < 10; p++) { + int digit = digits[p]; + if(digit == 0) + continue; + +#ifdef DEBUG + // at this stage the remaining digits should have 6 segments + if(count_segment(digit) != 6) + printf("digit has %d segments while 6 expected\n", count_segment(digit)); +#endif + + int segments_five_and_one = digits_code[5] | digits_code[1]; + if((segments_five_and_one & digit) == segments_five_and_one) { + digits_code[9] = digit; // this is 9 (6 segments and has those of 5 and 1) + digits[p] = 0; + } + else if((digits_code[5] & digit) == digits_code[5]) { + digits_code[6] = digit; // this is 6 (6 segments, has those of 5 but not 1) + digits[p] = 0; + } + else { + digits_code[0] = digit; // this is 0 + digits[p] = 0; + } + } + +#ifdef DEBUG + // check that we found all digits + for(int d = 0; d < 10; d++) { + if(digits_code[d] == 0) + printf("missing digit %d\n", d); + } +#endif + + // use the table to parse output digits + token = strtok(NULL, " "); // skip the '|' separator + int current_number = 0; + for(int n = 0; n < OUTPUT_DIGIT_SIZE && token != NULL; n++) { + int parsed_digit = parse_digit(token); + // search real digit + for(int d = 0; d < 10; d++) { + if(parsed_digit == digits_code[d]) { + current_number += (int) pow(10, OUTPUT_DIGIT_SIZE - 1 - n) * d; + break; + } + } + // next digit + token = strtok(NULL, " "); + } + sum += current_number; + //free(line); TODO causes memory corruption + } + CHECK(sum, EXPECTED2); +} + +int main() { + // read input + struct input_str input; + input_str_read(&input, INPUT); + + // do stuff + part1(&input); + part2(&input); + + // cleanup & exit + input_str_free(&input); + return 0; +} |