Add day 3

3 files changed, 498 insertions, 0 deletions

diff --git a/03/a.c b/03/a.c
new file mode 100644
index 0000000..caa1d60
--- /dev/null
+++ b/03/a.c
@@ -0,0 +1,69 @@
+#include <unistd.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#define BUF_SIZE 8192
+
+char buffer[BUF_SIZE];
+
+ssize_t read_to_buffer() {
+    ssize_t bytes = read(0, buffer, BUF_SIZE);
+    if (bytes < 0) {
+        printf("failed to read\n");
+        exit(1);
+    }
+    return bytes;
+}
+
+int tree(int position) {
+    if (buffer[position] == '.') {
+        return 0;
+    } else if (buffer[position] == '#') {
+        return 1;
+    } else {
+        printf("unknown character\n");
+        exit(1);
+    }
+}
+
+int file_position(int x, int y, int line_length) {
+    return (line_length + 2) * y + x;
+}
+
+int buffer_position(int x, int y, int line_length, int buffer_start) {
+    return file_position(x % line_length, y, line_length) - buffer_start;
+}
+
+int find_trees() {
+    int buffer_start = 0;
+    int line_length = 0;
+    int x = 0;
+    int y = 0;
+    ssize_t bytes = read_to_buffer();
+    int trees_hit = tree(0);
+
+    while (buffer[line_length] != '\r') {
+        line_length++;
+    }
+
+    int i = 2;
+    while (bytes) {
+        while (buffer_position(x + 3, y + 1, line_length, buffer_start) < bytes) {
+            y += 1;
+            x += 3;
+
+            trees_hit += tree(buffer_position(x, y, line_length, buffer_start));
+        }
+
+        buffer_start += bytes;
+        bytes = read_to_buffer();
+    }
+
+    return trees_hit;
+}
+
+int main() {
+    printf("%d\n", find_trees());
+}
diff --git a/03/b.c b/03/b.c
new file mode 100644
index 0000000..2f01601
--- /dev/null
+++ b/03/b.c
@@ -0,0 +1,106 @@
+#include <unistd.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#define BUF_SIZE 8192
+#define NUM_SLOPES 5
+
+char buffer[BUF_SIZE];
+
+struct Pair {
+    int x;
+    int y;
+};
+
+struct Pair slopes[NUM_SLOPES];
+
+ssize_t read_to_buffer() {
+    ssize_t bytes = read(0, buffer, BUF_SIZE);
+    return bytes;
+}
+
+int tree(int position) {
+    if (buffer[position] == '.') {
+        return 0;
+    } else if (buffer[position] == '#') {
+        return 1;
+    }
+}
+
+int file_position(int x, int y, int line_length) {
+    return (line_length + 2) * y + x;
+}
+
+int buffer_position(struct Pair pos, int line_length, int buffer_start) {
+    return file_position(pos.x % line_length, pos.y, line_length) - buffer_start;
+}
+
+long long int find_trees() {
+    int trees_hit[NUM_SLOPES];
+    struct Pair next_check[NUM_SLOPES];
+    for (int i = 0; i < NUM_SLOPES; i++) {
+        trees_hit[i] = 0;
+        next_check[i].x = slopes[i].x;
+        next_check[i].y = slopes[i].y;
+    }
+
+    int y = 0;
+
+    ssize_t bytes = read_to_buffer();
+    int buffer_start = 0;
+    int line_length = 0;
+    while (buffer[line_length] != '\r') {
+        line_length++;
+    }
+
+    while (bytes) {
+        int checked = 5;
+        while (checked == 5) {
+            checked = 0;
+            for (int i = 0; i < NUM_SLOPES; i++) {
+                int position = buffer_position(next_check[i], line_length, buffer_start);
+                if (position < bytes && position >= 0 && y == next_check[i].y) {
+                    trees_hit[i] += tree(position);
+
+                    next_check[i].x += slopes[i].x;
+                    next_check[i].x %= line_length;
+                    next_check[i].y += slopes[i].y;
+                        
+                    checked++;
+                } else if (position < 0 || y < next_check[i].y) {
+                    checked++;
+                }
+            }
+
+            if (checked == NUM_SLOPES) {
+                y++;
+            }
+        }
+
+        buffer_start += bytes;
+        bytes = read_to_buffer();
+    }
+
+    long long int res = 1;
+    for (int i = 0; i < NUM_SLOPES; i++) {
+        res *= trees_hit[i];
+    }
+
+    return res;
+}
+
+int main() {
+    slopes[0].x = 1;
+    slopes[0].y = 1;
+    slopes[1].x = 3;
+    slopes[1].y = 1;
+    slopes[2].x = 5;
+    slopes[2].y = 1;
+    slopes[3].x = 7;
+    slopes[3].y = 1;
+    slopes[4].x = 1;
+    slopes[4].y = 2;
+    printf("%lld\n", find_trees());
+}
diff --git a/03/input.txt b/03/input.txt
new file mode 100644
index 0000000..104bc3d
--- /dev/null
+++ b/03/input.txt
@@ -0,0 +1,323 @@
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