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/*!
\file dfkvkselect.c
\brief Sorts only the largest k values
\date Started 7/14/00
\author George
\version\verbatim $Id: fkvkselect.c 10711 2011-08-31 22:23:04Z karypis $\endverbatim
*/
#include <GKlib.h>
/* Byte-wise swap two items of size SIZE. */
#define QSSWAP(a, b, stmp) do { stmp = (a); (a) = (b); (b) = stmp; } while (0)
/******************************************************************************/
/*! This function puts the 'topk' largest values in the beginning of the array */
/*******************************************************************************/
int gk_dfkvkselect(size_t n, int topk, gk_fkv_t *cand)
{
int i, j, lo, hi, mid;
gk_fkv_t stmp;
float pivot;
if (n <= topk)
return n; /* return if the array has fewer elements than we want */
for (lo=0, hi=n-1; lo < hi;) {
mid = lo + ((hi-lo) >> 1);
/* select the median */
if (cand[lo].key < cand[mid].key)
mid = lo;
if (cand[hi].key > cand[mid].key)
mid = hi;
else
goto jump_over;
if (cand[lo].key < cand[mid].key)
mid = lo;
jump_over:
QSSWAP(cand[mid], cand[hi], stmp);
pivot = cand[hi].key;
/* the partitioning algorithm */
for (i=lo-1, j=lo; j<hi; j++) {
if (cand[j].key >= pivot) {
i++;
QSSWAP(cand[i], cand[j], stmp);
}
}
i++;
QSSWAP(cand[i], cand[hi], stmp);
if (i > topk)
hi = i-1;
else if (i < topk)
lo = i+1;
else
break;
}
/*
if (cand[lo].key < cand[hi].key)
printf("Hmm Error: %d %d %d %f %f\n", i, lo, hi, cand[lo].key, cand[hi].key);
for (i=topk; i<n; i++) {
for (j=0; j<topk; j++)
if (cand[i].key > cand[j].key)
printf("Hmm Error: %d %d %f %f %d %d\n", i, j, cand[i].key, cand[j].key, lo, hi);
}
*/
return topk;
}
/******************************************************************************/
/*! This function puts the 'topk' smallest values in the beginning of the array */
/*******************************************************************************/
int gk_ifkvkselect(size_t n, int topk, gk_fkv_t *cand)
{
int i, j, lo, hi, mid;
gk_fkv_t stmp;
float pivot;
if (n <= topk)
return n; /* return if the array has fewer elements than we want */
for (lo=0, hi=n-1; lo < hi;) {
mid = lo + ((hi-lo) >> 1);
/* select the median */
if (cand[lo].key > cand[mid].key)
mid = lo;
if (cand[hi].key < cand[mid].key)
mid = hi;
else
goto jump_over;
if (cand[lo].key > cand[mid].key)
mid = lo;
jump_over:
QSSWAP(cand[mid], cand[hi], stmp);
pivot = cand[hi].key;
/* the partitioning algorithm */
for (i=lo-1, j=lo; j<hi; j++) {
if (cand[j].key <= pivot) {
i++;
QSSWAP(cand[i], cand[j], stmp);
}
}
i++;
QSSWAP(cand[i], cand[hi], stmp);
if (i > topk)
hi = i-1;
else if (i < topk)
lo = i+1;
else
break;
}
/*
if (cand[lo].key > cand[hi].key)
printf("Hmm Error: %d %d %d %f %f\n", i, lo, hi, cand[lo].key, cand[hi].key);
for (i=topk; i<n; i++) {
for (j=0; j<topk; j++)
if (cand[i].key < cand[j].key)
printf("Hmm Error: %d %d %f %f %d %d\n", i, j, cand[i].key, cand[j].key, lo, hi);
}
*/
return topk;
}
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