X-Git-Url: http://mj.ucw.cz/gitweb/?a=blobdiff_plain;ds=sidebyside;f=ucw%2Fheap.h;h=e0a33b02a60968bd5e0d24003c7b43a3b59c6cfe;hb=aeb6304585a714ebff73955095d9b49863ebb199;hp=d8ef8d5c97cd7a6f1829917c8aa4c87a8bb94e3b;hpb=79b816d635673f2a195eee048473572b18b718c8;p=libucw.git

diff --git a/ucw/heap.h b/ucw/heap.h
index d8ef8d5c..e0a33b02 100644
--- a/ucw/heap.h
+++ b/ucw/heap.h
@@ -98,7 +98,7 @@
   } while(0)
 
 /**
- * Insert `heap[num + 1]` in `O(log(n))` time.
+ * Insert `heap[num]` in `O(log(n))` time. The value of @num must be increased before.
  **/
 #define HEAP_INSERT(type,heap,num,less,swap)						\
   do {											\
@@ -121,6 +121,19 @@
     HEAP_BUBBLE_DOWN_J(heap,num,less,swap);						\
   } while(0)
 
+/**
+ * If you need to decrease the value of `heap[pos]`, just do it and then call this macro to rebuild the heap.
+ * Only `heap[pos]` can be changed, the rest of the array must form a valid heap.
+ * The time complexity is `O(log(n))`.
+ **/
+#define HEAP_DECREASE(type,heap,num,less,swap,pos)					\
+  do {											\
+    uns _j, _u;										\
+    type x;										\
+    _j = pos;										\
+    HEAP_BUBBLE_UP_J(heap,num,less,swap);						\
+  } while(0)
+
 /**
  * Delete `heap[pos]` in `O(log(n))` time.
  **/