Day3 C

day3/c/day3.c

@@ -0,0 +1,155 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define LINE_MAX_LENGTH 256
+#define MAX_MAP_SIZE 1024
+#define MAX_NUMBERS 32*1024
+#define abs(a) ((a) < 0 ? -(a) : (a))
+
+struct num_position_t {
+    int x;
+    int y;
+    int length;
+    unsigned int value;
+};
+
+struct num_position_t* create_position(int x, int y, int length, unsigned int value);
+int has_adjacent_symbol(struct num_position_t* number, int symbol_map[MAX_MAP_SIZE][MAX_MAP_SIZE]);
+unsigned int gear_ratio(int x, int y, struct num_position_t** numbers, int num_numbers);
+
+int main() {
+    char *p, *buf, c, tmp[64];
+    struct num_position_t **numbers, *tmp_pos;
+    numbers = (struct num_position_t**)malloc(MAX_NUMBERS * sizeof(struct num_position_t*));
+
+    int symbol_map[MAX_MAP_SIZE][MAX_MAP_SIZE];
+    memset(symbol_map, 0, MAX_MAP_SIZE*MAX_MAP_SIZE*sizeof(int));
+
+    int num_numbers = 0, num_length = 0;
+    unsigned int curr = 0;
+    int x = 0, y = 0;
+
+    buf = (char *)malloc(LINE_MAX_LENGTH);
+    memset(buf, 0, LINE_MAX_LENGTH);
+    p = buf;
+
+    int map_x = 0;
+    int map_y = 0;
+
+    while ((c = getchar()) != EOF) {
+        *p++ = c;
+        if (c == '\n') {
+            p = buf;
+            while (*p != '\n') {
+                if (*p == '-' || *p == '+') {
+                    symbol_map[x][y] = 1;
+                    p++;
+                    x++;
+                } else if (sscanf(p, "%u", &curr) != 0) {
+                    num_length = sprintf(tmp, "%u", curr);
+                    tmp_pos = create_position(x, y, num_length, curr);
+                    numbers[num_numbers] = tmp_pos;
+                    num_numbers++;
+                    p += num_length;
+                    x += num_length;
+                } else {
+                    if (*p != '.') {
+                        symbol_map[x][y] = 1;
+                    }
+                    if (*p == '*') {
+                        symbol_map[x][y] = 2;
+                    }
+                    p++;
+                    x++;
+                }
+            }
+            map_x = x;
+            x = 0;
+            y++;
+            memset(buf, 0, LINE_MAX_LENGTH);
+            p = buf;
+        }
+    }
+
+    map_y = y;
+
+    // Part 1
+    unsigned int part1 = 0;
+
+    for (int i = 0; i < num_numbers; i++) {
+        if (has_adjacent_symbol(numbers[i], symbol_map)) {
+            part1 += numbers[i]->value;
+        }
+    }
+
+    printf("%u\n", part1);
+
+    // Part 2
+    unsigned int part2 = 0;
+
+    for (int i = 0; i < map_y; i++) {
+        for (int j = 0; j < map_x; j++) {
+            if (symbol_map[j][i] == 2) {
+                part2 += gear_ratio(j, i, numbers, num_numbers);
+            }
+        }
+    }
+
+    printf("%u\n", part2);
+
+    free(buf);
+    for (int i = 0; i < num_numbers; i++) {
+        free(numbers[i]);
+    }
+    free(numbers);
+}
+
+struct num_position_t* create_position(int x, int y, int length, unsigned int value) {
+    struct num_position_t *pos;
+    pos = (struct num_position_t*)malloc(sizeof(struct num_position_t));
+    pos->x = x;
+    pos->y = y;
+    pos->length = length;
+    pos->value = value;
+    return pos;
+}
+
+int has_adjacent_symbol(struct num_position_t* number, int symbol_map[MAX_MAP_SIZE][MAX_MAP_SIZE]) {
+    int x, y;
+    for (int i = 0; i < number->length; i++) {
+        for (int j = -1; j <= 1; j++) {
+            for (int k = -1; k <= 1; k++) {
+                x = number->x + i + j;    
+                y = number->y + k;    
+                if (x < 0 || y < 0) continue;
+                if (symbol_map[x][y]) return 1;
+            }
+        }
+    }
+
+    return 0;
+}
+
+unsigned int gear_ratio(int x, int y, struct num_position_t** numbers, int num_numbers) {
+    int gear_num = 0;
+    unsigned int num_parts[2];
+    for (int i = 0; i < num_numbers; i++) {
+        for (int j = 0; j < numbers[i]->length; j++) {
+            if (abs(numbers[i]->x + j - x) <= 1 && abs(numbers[i]->y - y) <= 1) {
+                // Not a gear
+                if (gear_num == 2) return 0;
+                // Add gear
+                num_parts[gear_num] = numbers[i]->value;
+                gear_num++;
+                break;
+            }
+        }
+    }
+
+    if (gear_num == 2) {
+        return num_parts[0] * num_parts[1];
+    }
+
+    return 0;
+}