130 lines
3.1 KiB
C
130 lines
3.1 KiB
C
#include <stdio.h>
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#include <stdint.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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#define STRBUF_SIZE 200
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#define DEFAULT_FILE "input.txt"
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#define ISDIGIT(X) (X >= '0' && X <= '9')
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// Parses a found number.
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// The provided location can be any digit of the
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// number; this function will automatically
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// seek the first digit before processing.
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// Erases numbers as they are processed.
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uint16_t parse_num_at(char *str, uint8_t idx)
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{
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// Check input
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if (str[idx] < '0' || str[idx] > '9') return 0;
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// Find first digit of number
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while (ISDIGIT(str[idx]) && idx) idx--;
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if (!ISDIGIT(str[idx])) idx++;
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uint16_t num = 0;
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// Add up all digits
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while (ISDIGIT(str[idx]))
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{
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num = (num * 10) + (str[idx] - '0');
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// Erase the number to make sure we don't count it twice
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str[idx] = '.';
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idx++;
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}
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return num;
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}
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// Returns the sum of all numbers around a symbol,
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// including diagonals.
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uint16_t search_numbers_around( uint8_t idx,
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char *above,
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char *current,
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char *below)
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{
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uint16_t sum = 0;
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if (idx) sum += parse_num_at(above, idx - 1);
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sum += parse_num_at(above, idx);
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sum += parse_num_at(above, idx + 1);
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sum += parse_num_at(current, idx + 1);
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sum += parse_num_at(current, idx - 1);
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if (idx) sum += parse_num_at(below, idx - 1);
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sum += parse_num_at(below, idx);
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sum += parse_num_at(below, idx + 1);
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return sum;
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}
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// Search through a line of *current for symbols.
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// returns the sum for that line (erases numbers as
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// they are processed.)
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uint16_t parse_line(char *above, char *current, char *below)
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{
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uint16_t sum = 0;
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uint8_t idx;
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char c;
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for (idx = 0; current[idx] != 0; idx++)
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{
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c = current[idx];
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if (!ISDIGIT(c) && c != '.' && c != '\n')
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{
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// We've found a symbol,
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// add up all numbers around it
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sum += search_numbers_around(idx, above, current, below);
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}
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}
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return sum;
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}
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int main(int argc, char **argv)
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{
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// Get filename as an argument, defaults to "input.txt"
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char *path = (argc > 1) ? argv[1] : DEFAULT_FILE;
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if (!path)
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{
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printf("Requires input file.\n");
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return 1;
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}
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FILE *file = fopen(path, "r");
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if (!file)
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{
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printf("Could not find file.");
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return 1;
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}
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char *above = malloc(sizeof(char) * STRBUF_SIZE);
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char *current = malloc(sizeof(char) * STRBUF_SIZE);
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char *below = malloc(sizeof(char) * STRBUF_SIZE);
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memset(above, '.', STRBUF_SIZE);
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fgets(current, STRBUF_SIZE, file);
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uint32_t sum = 0;
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while (fgets(below, 200, file))
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{
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sum += parse_line(above, current, below);
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free(above);
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above = current;
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current = below;
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below = malloc(sizeof(char) * STRBUF_SIZE);
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memset(below, '.', STRBUF_SIZE);
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}
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// Process the last line of the file
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sum += parse_line(above, current, below);
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printf("Sum: %d\n", sum);
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return 0;
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} |