1 files changed, 113 insertions, 0 deletions
diff --git a/Advent-of-Code-2022/aoc-9/main.c b/Advent-of-Code-2022/aoc-9/main.c
new file mode 100644
index 0000000..00945eb
--- /dev/null
+++ b/Advent-of-Code-2022/aoc-9/main.c
@@ -0,0 +1,113 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#if 0
+  #define KNOTS 2
+#else
+  #define KNOTS 10
+#endif
+
+#if 0
+  #define FILENAME "sample.txt"
+#else
+  #define FILENAME "input.txt"
+#endif
+
+#define SIDE 1000
+#define OFFSET (SIDE/2)
+
+typedef enum {
+    NONE = 0,
+    NORTH = 1,
+    SOUTH = -1,
+    EAST = 1,
+    WEST = -1
+} direction;
+
+int board[SIDE][SIDE] = {0};
+int rope[KNOTS][2] = {0};
+direction rope_dir[KNOTS][2] = {0};
+
+void move(int k)
+{
+    rope[k][0] += rope_dir[k][0];
+    rope[k][1] += rope_dir[k][1];
+}
+
+void parse_dir(char d)
+{
+    rope_dir[0][0] = NONE;
+    rope_dir[0][1] = NONE;
+
+    switch(d) {
+    case 'U':
+        rope_dir[0][1] = NORTH;
+        return;
+    case 'D':
+        rope_dir[0][1] = SOUTH;
+        return;
+    case 'R':
+        rope_dir[0][0] = EAST;
+        return;
+    case 'L':
+        rope_dir[0][0] = WEST;
+        return;
+    }
+}
+
+void parse()
+{
+    FILE *fp = fopen(FILENAME, "r");
+    if(!fp) {
+        fprintf(stderr, "ERROR: Could not open file: %s\n", FILENAME);
+        exit(1);
+    }
+
+    char line[256];
+    while(fgets(line, sizeof(line), fp))
+    {
+        parse_dir(strtok(line, " ")[0]);
+        int n = atoi(strtok(NULL, " "));
+
+        for(int i = 0; i < n; i++)
+        {
+            move(0);
+            for(int j = 1; j < KNOTS; j++)
+            {
+                int hor  = rope[j-1][0] - rope[j][0];
+                if(hor > 0) rope_dir[j][0] = EAST;
+                else if(hor < 0) rope_dir[j][0] = WEST;
+                else rope_dir[j][0] = NONE;
+
+                int vert = rope[j-1][1] - rope[j][1];
+                if(vert > 0) rope_dir[j][1] = NORTH;
+                else if(vert < 0) rope_dir[j][1] = SOUTH;
+                else rope_dir[j][1] = NONE;
+
+                if(abs(vert) > 1 || abs(hor) > 1)
+                    move(j);
+            }
+
+            board[rope[KNOTS-1][0] + OFFSET][rope[KNOTS-1][1] + OFFSET]++;
+        }
+    }
+
+    fclose(fp);
+}
+
+int sum()
+{
+    int sum = 0;
+    for(int i = 0; i < SIDE; i++)
+        for(int j = 0; j < SIDE; j++)
+            if(board[j][i] > 0) sum++;
+    return sum;
+}
+
+int main(void)
+{
+    parse();
+    printf("%d\n", sum());
+    return 0;
+}