93 lines
1.7 KiB
C
93 lines
1.7 KiB
C
#include <stdlib.h>
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#include <search.h>
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#include "tsearch.h"
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static inline int height(struct node *n) { return n ? n->h : 0; }
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static int rot(void **p, struct node *x, int dir /* deeper side */)
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{
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struct node *y = x->a[dir];
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struct node *z = y->a[!dir];
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int hx = x->h;
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int hz = height(z);
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if (hz > height(y->a[dir])) {
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/*
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* x
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* / \ dir z
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* A y / \
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* / \ --> x y
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* z D /| |\
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* / \ A B C D
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* B C
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*/
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x->a[dir] = z->a[!dir];
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y->a[!dir] = z->a[dir];
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z->a[!dir] = x;
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z->a[dir] = y;
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x->h = hz;
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y->h = hz;
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z->h = hz+1;
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} else {
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/*
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* x y
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* / \ / \
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* A y --> x D
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* / \ / \
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* z D A z
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*/
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x->a[dir] = z;
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y->a[!dir] = x;
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x->h = hz+1;
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y->h = hz+2;
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z = y;
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}
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*p = z;
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return z->h - hx;
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}
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/* balance *p, return 0 if height is unchanged. */
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int __tsearch_balance(void **p)
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{
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struct node *n = *p;
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int h0 = height(n->a[0]);
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int h1 = height(n->a[1]);
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if (h0 - h1 + 1u < 3u) {
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int old = n->h;
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n->h = h0<h1 ? h1+1 : h0+1;
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return n->h - old;
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}
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return rot(p, n, h0<h1);
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}
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void *tsearch(const void *key, void **rootp,
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int (*cmp)(const void *, const void *))
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{
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if (!rootp)
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return 0;
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void **a[MAXH];
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struct node *n = *rootp;
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struct node *r;
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int i=0;
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a[i++] = rootp;
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for (;;) {
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if (!n)
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break;
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int c = cmp(key, n->key);
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if (!c)
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return n;
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a[i++] = &n->a[c>0];
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n = n->a[c>0];
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}
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r = malloc(sizeof *r);
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if (!r)
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return 0;
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r->key = key;
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r->a[0] = r->a[1] = 0;
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r->h = 1;
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/* insert new node, rebalance ancestors. */
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*a[--i] = r;
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while (i && __tsearch_balance(a[--i]));
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return r;
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}
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