/*
* *
* Copyright (C) 2008 Bert Huang
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see .
*/
#include
int recursiveSelect(float *V, int *inds, int start, int end, int k)
{
/*recursively partitions vector V to find kth element */
int pivot, i, tmp;
float tmpdbl;
if (start==end-1) /* active set is only one entry */
return inds[start];
/*otherwise pick pivot and split */
pivot = start;
for (i=start+1; iV[pivot]) {
/* first move pivot value up one index */
tmp = inds[pivot];
tmpdbl = V[pivot];
inds[pivot] = inds[pivot+1];
V[pivot] = V[pivot+1];
inds[pivot+1] = tmp;
V[pivot+1] = tmpdbl;
if (i>pivot+1) {
/* now we need to swap i th with pivot-1 th */
tmp = inds[pivot];
tmpdbl = V[pivot];
inds[pivot] = inds[i];
V[pivot] = V[i];
inds[i] = tmp;
V[i] = tmpdbl;
}
pivot++;
}
}
if (pivot==k)
return inds[pivot];
/* now we decide if kth is to the right of the pivot or the left */
else if (pivot > k) {
return recursiveSelect(V,inds,start,pivot,k);
} else {
return recursiveSelect(V,inds,pivot+1,end,k);
}
}
int quickselect(float *V, int N, int k)
{
/* returns the index of the kth greatest value in vector V */
float *Vcopy;
int i, *inds, ret;
if (k>=N) {
return -1;
}
if (k<0) {
return -1;
}
Vcopy = (float*)malloc(N*sizeof(float));
inds = (int*)malloc(N*sizeof(int));
for (i=0; i