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/* ========================================================================== */
/* === Source/Mongoose_QPMinHeap.cpp ======================================== */
/* ========================================================================== */
/* -----------------------------------------------------------------------------
* Mongoose Graph Partitioning Library Copyright (C) 2017-2018,
* Scott P. Kolodziej, Nuri S. Yeralan, Timothy A. Davis, William W. Hager
* Mongoose is licensed under Version 3 of the GNU General Public License.
* Mongoose is also available under other licenses; contact authors for details.
* -------------------------------------------------------------------------- */
/* ========================================================================== */
/* === minheap ============================================================== */
/* ========================================================================== */
#include "Mongoose_QPMinHeap.hpp"
#include "Mongoose_Internal.hpp"
namespace Mongoose
{
/* ========================================================================== */
/* === QPMinHeap_build ====================================================== */
/* ========================================================================== */
/* build a min heap in heap [1..nheap] */
void QPMinHeap_build(Int *heap, /* on input, an unsorted set of elements */
Int size, /* number of elements to build into the heap */
double *x)
{
Int p;
for (p = size / 2; p >= 1; p--)
{
QPMinHeapify(p, heap, size, x);
}
}
/* ========================================================================== */
/* === QPMinHeap_delete ===================================================== */
/* ========================================================================== */
/* delete the top element in a min heap */
Int QPMinHeap_delete /* return new size of heap */
(Int *heap, /* containing indices into x, 1..n on input */
Int size, /* number of items in heap */
const double *x /* not modified */
)
{
if (size <= 1)
{
return (0);
}
/* move element from the end of the heap to the top */
heap[1] = heap[size];
size--;
QPMinHeapify(1, heap, size, x);
return (size);
}
/* ========================================================================== */
/* === QPMinHeap_add ======================================================== */
/* ========================================================================== */
/* add a new leaf to a min heap */
Int QPMinHeap_add(
Int leaf, /* the new leaf */
Int *heap, /* size n, containing indices into x */
const double *x, /* not modified */
Int nheap /* number of elements in heap not counting new one */
)
{
Int l, lnew, lold;
double xold;
nheap++;
lold = nheap;
heap[lold] = leaf;
xold = x[leaf];
while (lold > 1)
{
lnew = lold / 2;
l = heap[lnew];
double xnew = x[l];
/* swap new and old */
if (xnew > xold)
{
heap[lnew] = leaf;
heap[lold] = l;
}
else
{
return (nheap);
}
lold = lnew;
}
return (nheap);
}
/* ========================================================================== */
/* === QPMinHeapify ========================================================= */
/* ========================================================================== */
/* heapify starting at vertex p. On input, the heap at vertex p satisfies */
/* the heap property, except for heap [p] itself. On output, the whole heap */
/* satisfies the heap property. */
void QPMinHeapify(Int p, /* start at vertex p in the heap */
Int *heap, /* size n, containing indices into x */
Int size, /* heap [ ... nheap] is in use */
const double *x /* not modified */
)
{
Int left, right, e, hleft, hright;
double xe, xleft, xright;
e = heap[p];
xe = x[e];
while (true)
{
left = p * 2;
right = left + 1;
if (right <= size)
{
hleft = heap[left];
hright = heap[right];
xleft = x[hleft];
xright = x[hright];
if (xleft < xright)
{
if (xe > xleft)
{
heap[p] = hleft;
p = left;
}
else
{
heap[p] = e;
return;
}
}
else
{
if (xe > xright)
{
heap[p] = hright;
p = right;
}
else
{
heap[p] = e;
return;
}
}
}
else
{
if (left <= size)
{
hleft = heap[left];
xleft = x[hleft];
if (xe > xleft)
{
heap[p] = hleft;
p = left;
}
}
heap[p] = e;
return;
}
}
}
} // end namespace Mongoose
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