Heap.h

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/******************************************************************************************[Heap.h]
Copyright (c) 2003-2006, Niklas Een, Niklas Sorensson
Copyright (c) 2007-2010, Niklas Sorensson
 
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#ifndef Minisat_Heap_h
#define Minisat_Heap_h
 
#include "Vec.h"
 
namespace Minisat
{
    //=================================================================================================
    // A heap implementation with support for decrease/increase key.
 
    template<class Comp>
    class Heap
    {
        Comp     lt;    // The heap is a minimum-heap with respect to this comparator
        vec<int> heap;    // Heap of integers
        vec<int> indices;    // Each integers position (index) in the Heap
 
        // Index "traversal" functions
        static inline int left( int i )
        {
            return i * 2 + 1;
        }
 
        static inline int right( int i )
        {
            return (i + 1) * 2;
        }
 
        static inline int parent( int i )
        {
            return (i - 1) >> 1;
        }
 
        void percolateUp( int i )
        {
            int x = heap[i];
            int p = parent( i );
 
            while( i != 0 && lt( x, heap[p] ) )
            {
                heap[i]          = heap[p];
                indices[heap[p]] = i;
                i                = p;
                p                = parent( p );
            }
            heap[i]    = x;
            indices[x] = i;
        }
 
        void percolateDown( int i )
        {
            int x = heap[i];
            while( left( i ) < heap.size() )
            {
                int child = right( i ) < heap.size() && lt( heap[right( i )], heap[left( i )] ) ? right( i ) : left( i );
                if( !lt( heap[child], x ) )
                    break;
                heap[i]          = heap[child];
                indices[heap[i]] = i;
                i                = child;
            }
            heap[i]    = x;
            indices[x] = i;
        }
 
        public:
            Heap( const Comp& c ):
                lt( c )
            {}
 
            int size() const
            {
                return heap.size();
            }
 
            bool empty() const
            {
                return heap.size() == 0;
            }
 
            bool inHeap( int n ) const
            {
                return n < indices.size() && indices[n] >= 0;
            }
 
            int operator []( int index ) const
            {
                assert( index < heap.size() );
                return heap[index];
            }
 
            void decrease( int n )
            {
                assert( inHeap( n ) );
                percolateUp( indices[n] );
            }
 
            void increase( int n )
            {
                assert( inHeap( n ) );
                percolateDown( indices[n] );
            }
 
            // Safe variant of insert/decrease/increase:
            void update( int n )
            {
                if( !inHeap( n ) )
                    insert( n );
                else
                {
                    percolateUp( indices[n] );
                    percolateDown( indices[n] );
                }
            }
 
            void insert( int n )
            {
                indices.growTo( n + 1, -1 );
                assert( !inHeap( n ) );
 
                indices[n] = heap.size();
                heap.push( n );
                percolateUp( indices[n] );
            }
 
            int removeMin()
            {
                int x = heap[0];
                heap[0]          = heap.last();
                indices[heap[0]] = 0;
                indices[x]       = -1;
                heap.pop();
                if( heap.size() > 1 )
                    percolateDown( 0 );
                return x;
            }
 
            // Rebuild the heap from scratch, using the elements in 'ns':
            void build( vec<int>& ns )
            {
                for( int i = 0; i < heap.size(); i++ )
                    indices[heap[i]] = -1;
                heap.clear();
 
                for( int i = 0; i < ns.size(); i++ )
                {
                    indices[ns[i]] = i;
                    heap.push( ns[i] );
                }
 
                for( int i = heap.size() / 2 - 1; i >= 0; i-- )
                    percolateDown( i );
            }
 
            void clear( bool dealloc = false )
            {
                for( int i = 0; i < heap.size(); i++ )
                    indices[heap[i]] = -1;
                heap.clear( dealloc );
            }
            
            void print() const
            {
                std::cout << "Order heap:";
                for( int i = 0; i < heap.size(); i++ )
                    std::cout << " " << heap[i];
                std::cout << std::endl;
            }
    };
 
    //=================================================================================================
}
 
#endif