knapsack.c File Reference

#include "postgres.h"
#include <math.h>
#include <limits.h>
#include "lib/knapsack.h"
#include "nodes/bitmapset.h"
#include "utils/memutils.h"

Include dependency graph for knapsack.c:

Go to the source code of this file.

Functions
Bitmapset *	DiscreteKnapsack (int max_weight, int num_items, int *item_weights, double *item_values)

Function Documentation

DiscreteKnapsack()

Bitmapset * DiscreteKnapsack	(	int	max_weight,
		int	num_items,
		int *	item_weights,
		double *	item_values
	)

Definition at line 52 of file knapsack.c.

{
    MemoryContext local_ctx = AllocSetContextCreate(CurrentMemoryContext,
                                                    "Knapsack",
                                                    ALLOCSET_SMALL_SIZES);
    MemoryContext oldctx = MemoryContextSwitchTo(local_ctx);
    double     *values;
    Bitmapset **sets;
    Bitmapset  *result;
    int         i,
                j;
 
    Assert(max_weight >= 0);
    Assert(num_items > 0 && item_weights);
 
    values = palloc((1 + max_weight) * sizeof(double));
    sets = palloc((1 + max_weight) * sizeof(Bitmapset *));
 
    for (i = 0; i <= max_weight; ++i)
    {
        values[i] = 0;
        sets[i] = bms_make_singleton(num_items);
    }
 
    for (i = 0; i < num_items; ++i)
    {
        int         iw = item_weights[i];
        double      iv = item_values ? item_values[i] : 1;
 
        for (j = max_weight; j >= iw; --j)
        {
            int         ow = j - iw;
 
            if (values[j] <= values[ow] + iv)
            {
                /* copy sets[ow] to sets[j] without realloc */
                if (j != ow)
                    sets[j] = bms_replace_members(sets[j], sets[ow]);
 
                sets[j] = bms_add_member(sets[j], i);
 
                values[j] = values[ow] + iv;
            }
        }
    }
 
    MemoryContextSwitchTo(oldctx);
 
    result = bms_del_member(bms_copy(sets[max_weight]), num_items);
 
    MemoryContextDelete(local_ctx);
 
    return result;
}

References ALLOCSET_SMALL_SIZES, AllocSetContextCreate, Assert(), bms_add_member(), bms_copy(), bms_del_member(), bms_make_singleton(), bms_replace_members(), CurrentMemoryContext, i, j, MemoryContextDelete(), MemoryContextSwitchTo(), palloc(), and values.

Referenced by consider_groupingsets_paths().