Committing days 1-4

03/03.c

@@ -0,0 +1,130 @@
+#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;
+}
+
+// Returns the sum of all numbers around a symbol,
+// including diagonals.
+uint16_t search_numbers_around( uint8_t idx,
+                                char *above,
+                                char *current,
+                                char *below)
+{
+    uint16_t sum = 0;
+    if (idx) sum += parse_num_at(above, idx - 1);
+    sum += parse_num_at(above, idx);
+    sum += parse_num_at(above, idx + 1);
+
+    sum += parse_num_at(current, idx + 1);
+    sum += parse_num_at(current, idx - 1);
+
+    if (idx) sum += parse_num_at(below, idx - 1);
+    sum += parse_num_at(below, idx);
+    sum += parse_num_at(below, idx + 1);
+
+    return sum;
+}
+
+// Search through a line of *current for symbols.
+// returns the sum for that line (erases numbers as
+// they are processed.)
+uint16_t parse_line(char *above, char *current, char *below)
+{
+    uint16_t sum = 0;
+    uint8_t idx;
+    char c;
+
+    for (idx = 0; current[idx] != 0; idx++)
+    {
+        c = current[idx];
+        if (!ISDIGIT(c) && c != '.' && c != '\n')
+        {
+            // We've found a symbol,
+            // add up all numbers around it
+            sum += search_numbers_around(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);
+
+    uint32_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: %d\n", sum);
+
+    return 0;
+}