Index: aoc2024.c
==================================================================
--- aoc2024.c
+++ aoc2024.c
@@ -52,10 +52,52 @@
                       break;
         }
     }
     printf("The guard visits %u positions before leaving the area.\n", visited);
     // Part Two
+    unsigned rowblock = 0, colblock = 0, positions = 0;
+    int row_initial = (int)(linear_pos / size);
+    int col_initial = (int)(linear_pos % size);
+    for (;;) {
+        strcpy(data, savedmap);
+        if (data[linearize2d(size, (unsigned)rowblock, (unsigned)colblock)] == '.') {
+            data[linearize2d(size, (unsigned)rowblock, (unsigned)colblock)] = '#'; // block it
+            row_pos = row_initial; col_pos = col_initial;
+            deltarow = -1; deltacol = 0;
+            data[linearize2d(size, (unsigned)row_pos, (unsigned)col_pos)] = '1';
+            bool looping = false;
+            while (!looping && validpos(size, row_pos + deltarow, col_pos + deltacol)) {
+                switch (data[linearize2d(size, (unsigned)(row_pos+deltarow), (unsigned)(col_pos+deltacol))]) {
+                    default: puts("stepped on default"); exit(EXIT_FAILURE);
+                    case '#': if (data[linearize2d(size, (unsigned)(row_pos), (unsigned)(col_pos))] == '8') looping = true;
+                              rightturn(&deltarow, &deltacol);
+                              break;
+                    case '8': looping = true; break;
+                    case '.': data[linearize2d(size, (unsigned)(row_pos+deltarow), (unsigned)(col_pos+deltacol))] = '0';
+                              /*fallthrough*/
+                    case '1':
+                    case '2':
+                    case '3':
+                    case '4':
+                    case '5':
+                    case '6':
+                    case '7': data[linearize2d(size, (unsigned)(row_pos+deltarow), (unsigned)(col_pos+deltacol))]++;
+                              row_pos += deltarow;
+                              col_pos += deltacol;
+                              break;
+                }
+            }
+            if (looping) positions++;
+        }
+        colblock++;
+        if (colblock == size) {
+            colblock = 0;
+            rowblock++;
+            if (rowblock == size) break;
+        }
+    }
+    printf("You can obstruct %u different positions.\n", positions);
     free(savedmap);
 }
 
 /* === aoc202405 =======================================================
 ===================================================================== */