Add a path_reverse() function

3 files changed, 31 insertions, 0 deletions

diff --git a/main.c b/main.c
index 4347551..93dfc1e 100644
--- a/main.c
+++ b/main.c
@@ -186,6 +186,8 @@ int main(int argc, char **argv) {
          *
          *    [d]    - Switch algorithms (A* or Dijsktra's)
          *
+         *    [r]    - Reverse the path and switch start/end around
+         *
          *    [s]    - Save the map to a bmp file
          *
          *    [w]    - Open a map from a plaintext file
@@ -276,6 +278,10 @@ int main(int argc, char **argv) {
                       /* TODO: print time */
                       break;
 
+            case 'r':
+                      path_reverse(&path, width, height, &start_pos, &end_pos);
+                      break;
+
             case 'y':
             case 'o':
             case 'u':
diff --git a/path.c b/path.c
index d643167..19a9aaa 100644
--- a/path.c
+++ b/path.c
@@ -330,6 +330,29 @@ void path_free(Path path, size_t height) {
     free(path);
 }
 
+void path_reverse(Path *path, size_t width, size_t height, Position *start, Position *end) {
+    Path new_path = path_new(width, height);
+
+    Position cur = *end;
+    while (cur.x != start->x || cur.y != start->y) {
+        Position parent = (*path)[cur.y][cur.x];
+        new_path[parent.y][parent.x] = cur;
+        cur = parent;
+    }
+
+    /* Switch start and end around */
+    start->x = start->x ^ end->x;
+    end->x   = start->x ^ end->x;
+    start->x = start->x ^ end->x;
+
+    start->y = start->y ^ end->y;
+    end->y   = start->y ^ end->y;
+    start->y = start->y ^ end->y;
+
+    path_free(*path, height);
+    *path = new_path;
+}
+
 char **visited_new(size_t width, size_t height) {
     char **visited = malloc(sizeof(char*) * height);
     if (visited == NULL) return NULL;
diff --git a/path.h b/path.h
index ea812e8..4a2159f 100644
--- a/path.h
+++ b/path.h
@@ -19,6 +19,8 @@ size_t diagonal_distance(Position a, Position b);
 
 Path path_new(size_t width, size_t height);
 void path_free(Path path, size_t height);
+/* Reverses the path in place and switches start and end */
+void path_reverse(Path *path, size_t width, size_t height, Position *start, Position *end);
 
 /* Helper funcs for the visited array */
 char **visited_new(size_t width, size_t height);