Add a path_reverse() function

1 files changed, 23 insertions, 0 deletions

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;