1 files changed, 122 insertions, 0 deletions
diff --git a/Advent-of-Code-2020/AOC-3/main.c b/Advent-of-Code-2020/AOC-3/main.c
new file mode 100644
index 0000000..6690b5d
--- /dev/null
+++ b/Advent-of-Code-2020/AOC-3/main.c
@@ -0,0 +1,122 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <assert.h>
+
+#if 0
+#define PART_1
+#else
+#define PART_2
+#endif
+
+#if 0
+#define FILE_PATH "example.txt"
+#else
+#define FILE_PATH "input.txt"
+#endif
+
+int WIDTH  = 0;
+int HEIGHT = 0;
+#define BOARD_SZ ((WIDTH) * (HEIGHT))
+
+char *board;
+
+void parse()
+{
+    FILE *fp = fopen(FILE_PATH, "r");
+    if(!fp) {
+        fprintf(stderr, "ERROR: Could not open file: %s", FILE_PATH);
+    }
+
+    char ch;
+    int i = 0;
+    // calculate size of the board
+    while((ch = fgetc(fp)) != EOF)
+    {
+        if(ch != '\n') {
+            i++;
+            continue;
+        }
+
+        if(WIDTH == 0) WIDTH = i;
+    }
+    HEIGHT = i / WIDTH;
+    board = malloc(BOARD_SZ);
+
+    fseek(fp, 0, SEEK_SET);
+    i = 0;
+    while((ch = fgetc(fp)) != EOF)
+    {
+        if(ch == '\n') continue;
+
+        board[i] = ch;
+        i++;
+    }
+
+    fclose(fp);
+}
+
+size_t traverse_map()
+{
+#ifdef PART_1
+    int slope_x[1] = {3};
+    int slope_y[1] = {1};
+    #define SZ 1
+#endif
+#ifdef PART_2
+    int slope_x[5] = {1, 3, 5, 7, 1};
+    int slope_y[5] = {1, 1, 1, 1, 2};
+    #define SZ 5
+    size_t result = 1;
+#endif
+
+    int x, y;
+    size_t hit_trees;
+    for(int i = 0; i < SZ; i++)
+    {
+        x = 0;
+        y = 0;
+        hit_trees = 0;
+        while(y != (HEIGHT - 1))
+        {
+            x += slope_x[i];
+            y += slope_y[i];
+
+            if(x >= WIDTH)
+                x = x - WIDTH;
+
+            if(board[y * WIDTH + x] == '#')
+                hit_trees++;
+        }
+
+        #ifdef PART_2
+        result *= hit_trees;
+        #endif
+    }
+
+    #ifdef PART_1
+    return hit_trees;
+    #endif
+    #ifdef PART_2
+    return result;
+
+    #endif
+}
+
+void print_board()
+{
+    for(int i = 0; i < BOARD_SZ; i++)
+    {
+        printf("%c", board[i]);
+
+        if(i % WIDTH == (WIDTH - 1))
+            putc('\n', stdout);
+    }
+}
+
+int main(void)
+{
+    parse();
+    printf("You hit %ld trees", traverse_map());
+    free(board);
+    return 0;
+}