Package org.apache.lucene.util

Class LongHeap

  • public final class LongHeap
extends Object
    A min heap that stores longs; a primitive priority queue that like all priority queues maintains a partial ordering of its elements such that the least element can always be found in constant time. Put()'s and pop()'s require log(size). This heap provides unbounded growth via push(long), and bounded-size insertion based on its nominal maxSize via insertWithOverflow(long). The heap is a min heap, meaning that the top element is the lowest value of the heap.
    NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

    • Constructor Summary

      Constructors 
      Constructor Description
      LongHeap​(int maxSize)
      Create an empty priority queue of the configured initial size.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void clear()
      Removes all entries from the PriorityQueue.
      long get​(int i)
      Return the element at the ith location in the heap array.
      boolean insertWithOverflow​(long value)
      Adds a value to an LongHeap in log(size) time.
      long pop()
      Removes and returns the least element of the PriorityQueue in log(size) time.
      long push​(long element)
      Adds a value in log(size) time.
      void pushAll​(LongHeap other)  
      int size()
      Returns the number of elements currently stored in the PriorityQueue.
      long top()
      Returns the least element of the LongHeap in constant time.
      long updateTop​(long value)
      Replace the top of the pq with newTop.

    • Constructor Detail

      • LongHeap

        public LongHeap​(int maxSize)
        Create an empty priority queue of the configured initial size.
        Parameters:
        maxSize - the maximum size of the heap, or if negative, the initial size of an unbounded heap

    • Method Detail

      • push

        public final long push​(long element)
        Adds a value in log(size) time. Grows unbounded as needed to accommodate new values.
        Returns:
        the new 'top' element in the queue.

      • insertWithOverflow

        public boolean insertWithOverflow​(long value)
        Adds a value to an LongHeap in log(size) time. If the number of values would exceed the heap's maxSize, the least value is discarded.
        Returns:
        whether the value was added (unless the heap is full, or the new value is less than the top value)

      • top

        public final long top()
        Returns the least element of the LongHeap in constant time. It is up to the caller to verify that the heap is not empty; no checking is done, and if no elements have been added, 0 is returned.

      • pop

        public final long pop()
        Removes and returns the least element of the PriorityQueue in log(size) time.
        Throws:
        IllegalStateException - if the LongHeap is empty.

      • updateTop

        public final long updateTop​(long value)
        Replace the top of the pq with newTop. Should be called when the top value changes. Still log(n) worst case, but it's at least twice as fast to 
         pq.updateTop(value);
        instead of 
         pq.pop();
 pq.push(value);
        Calling this method on an empty LongHeap has no visible effect.
        Parameters:
        value - the new element that is less than the current top.
        Returns:
        the new 'top' element after shuffling the heap.

      • size

        public final int size()
        Returns the number of elements currently stored in the PriorityQueue.

      • clear

        public final void clear()
        Removes all entries from the PriorityQueue.

      • pushAll

        public void pushAll​(LongHeap other)

      • get

        public long get​(int i)
        Return the element at the ith location in the heap array. Use for iterating over elements when the order doesn't matter. Note that the valid arguments range from [1, size].