Remove an element from the middle of an std::heap

Question

I\'m using a priority queue as a scheduler with one extra requirement. I need to be able to cancel scheduled items. This equates to removing an item from the middle of the pri

Answer 1

How does your repair_heap() work? Here's my guess:

If your heap is defined by some iterator range, say (heapBegin, heapEnd). The element you want to remove is the root of some subtree of the heap, which is defined by some subrange (subHeapBegin, subHeapEnd). Use std::pop_heap(subHeapBegin, subHeapEnd), then if subHeapEnd != heapEnd, swap the values at *(subHeapEnd-1) and *(heapEnd-1), which should put your deleted item at the end of the heap container. Now you have to percolate the element at *(subHeapEnd-1) up in your subheap. If I haven't missed something, which is possible, then all that remains is to chop the end element off of the heap container.

Before going to the trouble of trying to code that correctly (I've skipped some details like calculating subHeapBegin and subHeapEnd), I'd run some tests to determine if make_heap() really slows you down. Big-O is useful, but it's not the same thing as actual execution time.