Committing days 1-4

03/03-part2.c

@@ -0,0 +1,158 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define STRBUF_SIZE     200
+#define DEFAULT_FILE    "input.txt"
+#define ISDIGIT(X)      (X >= '0' && X <= '9')
+
+// Parses a found number.
+// The provided location can be any digit of the
+// number; this function will automatically
+// seek the first digit before processing.
+// Erases numbers as they are processed.
+uint16_t parse_num_at(char *str, uint8_t idx)
+{
+
+    // Check input
+    if (str[idx] < '0' || str[idx] > '9') return 0;
+
+    // Find first digit of number
+    while (ISDIGIT(str[idx]) && idx) idx--;
+    if (!ISDIGIT(str[idx])) idx++;
+
+    uint16_t num = 0;
+
+    // Add up all digits
+    while (ISDIGIT(str[idx]))
+    {
+        num = (num * 10) + (str[idx] - '0');
+        // Erase the number to make sure we don't count it twice
+        str[idx] = '.';
+        idx++;
+    }
+
+    return num;
+}
+
+// If the character is a * with two adjacent numbers,
+// returns the gear ratio. Returns zero if the symbol
+// is not a gear.
+uint64_t get_gear_ratio( uint8_t idx,
+                                char *above,
+                                char *current,
+                                char *below)
+{
+    char *above_copy =   malloc(sizeof(char) * STRBUF_SIZE);
+    char *current_copy = malloc(sizeof(char) * STRBUF_SIZE);
+    char *below_copy =   malloc(sizeof(char) * STRBUF_SIZE);
+
+    memcpy(above_copy, above, STRBUF_SIZE);
+    memcpy(current_copy, current, STRBUF_SIZE);
+    memcpy(below_copy, below, STRBUF_SIZE);
+
+    uint16_t nums[8] = {0};
+
+    if (idx) nums[0] = parse_num_at(above_copy, idx - 1);
+    nums[1] = parse_num_at(above_copy, idx);
+    nums[2] = parse_num_at(above_copy, idx + 1);
+
+    nums[3] = parse_num_at(current_copy, idx + 1);
+    nums[4] = parse_num_at(current_copy, idx - 1);
+
+    if (idx) nums[5] = parse_num_at(below_copy, idx - 1);
+    nums[6] = parse_num_at(below_copy, idx);
+    nums[7] = parse_num_at(below_copy, idx + 1);
+
+    free(above_copy);
+    free(current_copy);
+    free(below_copy);
+
+    uint8_t i = 0;
+    uint16_t num1 = 0;
+    uint16_t num2 = 0;
+
+    for (i = 0; i < 8; i++)
+    {
+        // More than 2 adjacent numbers
+        if (nums[i] && num1 && num2) return 0;
+
+        // The second number
+        if (nums[i] && num1) num2 = nums[i];
+
+        // The first number
+        else if (nums[i]) num1 = nums[i];
+    }
+
+    return num1 * num2;
+}
+
+// Search through a line of *current for symbols.
+uint64_t parse_line(char *above, char *current, char *below)
+{
+    uint64_t sum = 0;
+    uint8_t idx;
+    char c;
+
+    for (idx = 0; current[idx] != 0; idx++)
+    {
+        c = current[idx];
+        if (c == '*')
+        {
+            // We've found a symbol,
+            // add up all numbers around it
+            sum += get_gear_ratio(idx, above, current, below);
+        }
+    }
+    
+    return sum;
+}
+
+int main(int argc, char **argv)
+{
+    // Get filename as an argument, defaults to "input.txt"
+    char *path = (argc > 1) ? argv[1] : DEFAULT_FILE;
+
+    if (!path)
+    {
+        printf("Requires input file.\n");
+        return 1;
+    }
+
+    FILE *file = fopen(path, "r");
+
+    if (!file)
+    {
+        printf("Could not find file.");
+        return 1;
+    }
+
+    char *above =   malloc(sizeof(char) * STRBUF_SIZE);
+    char *current = malloc(sizeof(char) * STRBUF_SIZE);
+    char *below =   malloc(sizeof(char) * STRBUF_SIZE);
+
+    memset(above, '.', STRBUF_SIZE);
+    fgets(current, STRBUF_SIZE, file);
+
+    uint64_t sum = 0;
+
+    while (fgets(below, 200, file))
+    {
+        sum += parse_line(above, current, below);
+
+        free(above);
+        above = current;
+        current = below;
+        below = malloc(sizeof(char) * STRBUF_SIZE);
+        memset(below, '.', STRBUF_SIZE);
+    }
+
+    // Process the last line of the file
+    sum += parse_line(above, current, below);
+
+    printf("Sum: %lud\n", sum);
+
+    return 0;
+}