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) {
        int i;
        for (i = 0; i < heap.size(); i++)
            indices[heap[i]] = -1;
        heap.clear();

        for (i = 0; i < ns.size(); i++){
            indices[ns[i]] = i;
            heap.push(ns[i]); }

        for (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); 
    }
};


//=================================================================================================
}

#endif