gno/usr.bin/sort/sortarray.c

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1996-01-28 00:52:48 +00:00
#ifdef __CCFRONT__
#include <14:pragma.h>
#endif
#include "common.h"
#include <string.h>
/*
* void sortarray(char **array, unsigned long n);
*
* Pre: <array> is a pointer to an array of pointers to NULL-terminated
* strings, and <n> is the number of elements in <array>
*
* Post: The strings in <array> are sorted lexicographically in ascending
* order, using the heapsort algorithm. This is an in-place
* non-recursive sort with behavior O[n*lg(n)] both on average
* and worst-case.
*/
void sortarray(char *array[], unsigned long n) {
long l, j, ir, i;
char *rra;
if (n==1) return; /* no need to sort one element */
--array; /* fudge since the algorithm was designed */
/* for a unit-indexing */
l = (n>>1) + 1;
ir = n;
/*
* The index l will be decremented from its initial value down to 0 during
* the heap creation phase. Once it reaches 0, the index ir will be
* decremented from its initial value down to 0 during the heap selection
* phase.
*/
for (;;) {
if (l > 1) /* still in creation phase */
rra = array[--l];
else { /* in selection phase */
rra= array[ir]; /* clear a space at the end of array */
array[ir] = array[1]; /* retire the top of the heap into it */
if (--ir == 1) { /* done with the last promotion */
array[1] = rra;
return;
}
}
i = l; /* set up to sift down element rra to its proper place */
j = l << 1;
while (j<=ir) {
if (j<ir && (strcmp(array[j],array[j+1])<0)) ++j;
if (strcmp(rra,array[j])<0) { /* demote rra */
array[i] = array[j];
i = j;
j += i;
} else j = ir + 1; /* this is rra's level; set j to terminate */
} /* the sift-down */
array[i] = rra;
}
}