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ternary_tree.c
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ternary_tree.c
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#include "ternary_tree.h"
#include <stdlib.h> /* malloc(), free(), realloc() */
#include <assert.h>
#include <stddef.h> /* NULL, size_t */
#include <string.h> /* strdup(), strlen() */
typedef TernaryNode Node;
/*--------------------------------------*/
/* Stack API */
/*--------------------------------------*/
typedef struct _Stack {
void **arr; /* Array */
size_t top; /* Top index */
size_t cap; /* Capacity */
} Stack;
inline static void stack_init(Stack *stk) {
stk->arr = NULL;
stk->top = 0;
stk->cap = 0;
}
/* Expand to double size larger than old */
inline static size_t stack_get_new_size(Stack *stk) {
return stk->cap == 0 ? 1 : stk->cap << 1;
}
inline static bool stack_push(Stack *stk, void *e) {
if (!e) return false;
if (stk->cap == stk->top) {
const size_t new_size = stack_get_new_size(stk);
void *new_arr = realloc(stk->arr, new_size * sizeof(stk->arr[0]));
if (!new_arr)
return false;
stk->cap = new_size;
stk->arr = (void**)new_arr;
}
stk->arr[stk->top++] = e;
return true;
}
inline static void *stack_pop(Stack *stk) {
if (stk->top > 0)
return stk->arr[--stk->top];
return NULL;
}
inline static void stack_free(Stack *stk) {
free(stk->arr);
stk->arr = NULL;
stk->top = stk->cap = 0;
}
/* Get logical next node of \p node */
inline static Node **ternary_get_next_node(Node *node, char const **str) {
assert(str);
assert(*str);
assert(node);
const int diff = node->c - **str;
if (diff < 0)
return &(node->right);
else if (diff > 0)
return &(node->left);
/* Equal to the current character */
(*str)++; /* Forward */
return &(node->mid);
}
inline static Node *ternary_new_node(char c) {
Node *node = (Node*)malloc(sizeof(Node));
if (!node) return NULL;
node->c = c;
node->store = false;
node->left = node->mid = node->right = NULL;
return node;
}
char *ternary_search(TernaryNode const *root, char const *str) {
if (!str) return NULL;
int diff = 0;
while (root) {
diff = root->c - *str;
if (diff > 0)
root = root->left;
else if (diff < 0)
root = root->right;
else {
/* Allow empty string */
if (!*str) {
/* The last node of path, i.e. matching string */
if (!root->c)
return (char *)root->mid;
else break; /* Prefix of another string */
}
++str;
root = root->mid;
}
}
/* No such string exists */
return NULL;
}
char *ternary_add(Node **root, char const *str, bool store) {
if (!root || !str) return NULL;
Node **pcur = root;
Node *cur = NULL;
/* duplicate or store it in the last node */
char const *str_dup = str;
/* Check the str if is a duplicate */
while ((cur = *pcur)) {
/** string exists */
if (!*str && !cur->c) {
return (char*)(cur->mid);
}
pcur = ternary_get_next_node(cur, &str);
}
/* str may be a:
* * new string with unique suffix
* * prefix of another string
*
* Construct a string path along the mid pointer.
*
* The last node store string in its mid pointer.
* To support the property, it must be a special and
* unique node.
* Otherwise, the prefix of another string insert will be
* difficult.
*
* To identify it is the last node, set its stored charater to
* be 0 that is convenient for checking comparison of node->c and *str
*/
while ((*pcur = ternary_new_node(*str))) {
cur = *pcur;
if (!*str++) {
assert(cur->c == 0);
cur->store = store;
cur->mid = (Node*)(store ? strdup(str_dup) : str_dup);
return (char*)str;
}
pcur = &cur->mid;
}
return NULL;
}
static void search_match_str(Node const *root, ternary_str_callback cb, void *args, size_t *num, size_t max_num) {
if (!root || *num >= max_num) return;
search_match_str(root->left, cb, args, num, max_num);
if (!root->c) {
*num += 1;
cb((char const *)root->mid, args);
} else
search_match_str(root->mid, cb, args, num, max_num);
search_match_str(root->right, cb, args, num, max_num);
}
void ternary_search_prefix_num(Node const *root, char const *prefix, ternary_str_callback cb, void *args, size_t num) {
if (!root || !prefix) return;
/* If prefix is empty string, process all strings */
if (!*prefix) {
size_t n = 0;
search_match_str(root, cb, args, &n, num);
return;
}
int diff = 0;
while (root) {
diff = root->c - *prefix;
if (diff < 0)
root = root->right;
else if (diff > 0)
root = root->left;
else {
/* Search matching string in the subtree rooted
* by the mid pointer of the node with the last
* character of str recursively
*
* Because prefix just a slice of existed string
* in the tree, we must stop when meeting the last
* character
*/
root = root->mid;
if (*(++prefix) == 0) {
size_t n = 0;
search_match_str(root, cb, args, &n, num);
break;
}
}
if (!*prefix)
break;
}
}
static void ternary_free_(Node *root) {
if (root->left)
ternary_free_(root->left);
if (root->c && root->mid) {
ternary_free_(root->mid);
}
if (root->right)
ternary_free_(root->right);
if (root->store)
free(root->mid);
free(root);
}
void ternary_free(Node **root) {
if (!root) return;
if (*root)
ternary_free_(*root);
else
*root = NULL;
}
static bool ternary_node_is_no_child(Node *node) {
return !(node->left || node->right || node->mid);
}
static void ternary_remove_(Node **root, Stack *stk) {
/* Free the mid of the last node if insert in STORE mode */
assert(stk->top != 0);
Node **pvictim = (Node **)stack_pop(stk);
Node *victim = *pvictim;
assert(!victim->c);
if (victim->store)
free(victim->mid);
victim->mid = NULL; /* Must set NULL to make checking no child normally */
while (ternary_node_is_no_child(victim)) {
free(victim);
if (pvictim == root) {
*root = NULL;
return;
}
*pvictim = NULL;
pvictim = (Node **)stack_pop(stk);
victim = *pvictim;
}
/* Current, the victim is the first node with child */
/* The node in a prefix path of another string,
* we can't free it
*/
if (victim->mid) return;
if (victim->left && victim->right) {
/* Transplant:
* victim
* / \
* left right
* / | \
* * * nil
* left replace victim and set right
*/
if (!victim->left->right) {
victim->left->right = victim->right;
*pvictim = victim->left;
} else if (!victim->right->left) {
/* symmetric case */
victim->right->left = victim->left;
*pvictim = victim->right;
} else return;
/*
* victim
* / \
* left right
* / | \
* * * *
*
* If victim->left->right is not NULL,
* ratation may be complex.
*
* Can't to transplant, just leave in the tree
* and as a sentinel.
*/
} else if (victim->right) {
// left is NULL
*pvictim = victim->right;
} else if (victim->left) {
// right is NULL
*pvictim = victim->left;
}
free(victim);
}
bool ternary_remove(Node **root, char const *str) {
if (!root || !str) return false;
Node **pcur = root;
Node *cur = NULL;
Stack node_stk;
stack_init(&node_stk);
/* If str exists in the tree,
* we must push all nodes in the path
* to the stack since we don't know the longest
* prefix of str in the tree.
*/
while ((cur = *pcur)) {
stack_push(&node_stk, pcur);
/* The string path has pushed to stack */
if (!*str && !cur->c) {
ternary_remove_(root, &node_stk);
stack_free(&node_stk);
return true;
}
pcur = ternary_get_next_node(cur, &str);
}
stack_free(&node_stk);
return false;
}