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