lander/tries/src/ternarytrie.c

#include "ternarytrie.h"
#include "ternarytrie_node.c"
#include <stdint.h>
#include <stdlib.h>
#include <string.h>

typedef struct ttrie {
  TernaryTrieNode *root;
  size_t size;
} TernaryTrie;

/**
 * Allocate and initialize an empty TernaryTrie
 *
 * @return pointer to the empty TernaryTrie
 */
TernaryTrie *ternarytrie_init() {
  TernaryTrie *node = calloc(1, sizeof(TernaryTrie));
  node->root = ttnode_init();

  return node;
}

/**
 * De-allocate a TernaryTree by freeing its entire underlying structure.
 *
 * @param trie trie to free
 */
void ternarytrie_free(TernaryTrie *trie) {
  ttnode_free(trie->root);
  free(trie);
}

typedef struct searchresult {
  TernaryTrieNode *parent;
  TernaryTrieNode *child;
} SearchResult;

SearchResult ternarytrie_search_node(TernaryTrie *trie, const char *string) {
  SearchResult out = {NULL, NULL};

  // Edge case for empty string
  if (string[0] == DELIMITER) {
    if (trie->root->type == 1) {
      out.child = trie->root;
    }

    return out;
  }

  size_t i = 0;
  TernaryTrieNode **node_ptr = &(trie->root);
  TernaryTrieNode **child_ptr;

  do {
    child_ptr = ttnode_search(*node_ptr, string[i], false);

    // We don't have to check whether *node_ptr is NULL, because if it was
    // NULL, it wouldn't be in the binary tree.
    if (child_ptr == NULL || *child_ptr == NULL) {
      return out;
    }

    i++;

    if (string[i] == DELIMITER || (*child_ptr)->type == 2) {
      break;
    }

    node_ptr = child_ptr;
  } while (1);

  if ((*child_ptr)->type == 2) {
    if (string[i] != DELIMITER &&
        strcmp(string + i, (*child_ptr)->ptr.string) == 0) {
      out.child = *child_ptr;
      out.parent = *node_ptr;
    }
  }
  // Here we know we've traversed through the entire string and have arrived at
  // a node that isn't a full leaf
  else if ((*child_ptr)->type == 1) {
    out.child = *child_ptr;
    out.parent = *node_ptr;
  }

  return out;
}

/**
 * Returns whether the given string is present in the trie.
 *
 * @param trie trie to look in
 * @param string string to look up
 * @return true if the string is present in the trie, false otherwise
 */
bool ternarytrie_search(TernaryTrie *trie, const char *string) {
  SearchResult res = ternarytrie_search_node(trie, string);

  return res.child != NULL;
}

/**
 * Add the given string to the TernaryTrie.
 *
 * @param trie trie to add string to
 * @param string string to add
 * @return true if the string wasn't present in the trie and thus added, false
 * otherwise
 */
bool ternarytrie_add(TernaryTrie *trie, const char *string) {
  // Edge case for empty string
  if (string[0] == DELIMITER) {
    if (trie->root->type == 0) {
      trie->root->type = 1;
      trie->size++;

      return true;
    }

    return false;
  }

  size_t i = 0;
  TernaryTrieNode **node_ptr = &(trie->root);
  TernaryTrieNode **new_node_ptr;

  do {
    new_node_ptr = ttnode_search(*node_ptr, string[i], true);

    // ttnode_search will only return NULL with create true if the node to look
    // in represents a full leaf. Therefore, we split the node and restart the
    // iteration.
    if (new_node_ptr == NULL) {
      // It's possible we've ended up in the full leaf node that represents this
      // string
      if (strcmp(string + i, (*node_ptr)->ptr.string) == 0) {
        return false;
      }

      ttnode_split(*node_ptr);
      continue;
    }

    node_ptr = new_node_ptr;

    // The search function has added the character to the node
    i++;

    // The next node in the string's path doesn't exist yet, so we add it to the
    // trie
    if (*node_ptr == NULL) {
      TernaryTrieNode *new_node = ttnode_init();

      // If there's a remaining part of the string, we add it to the leaf
      if (string[i] != DELIMITER) {
        ttnode_set_string(new_node, string + i);
      } else {
        new_node->type = 1;
      }

      *node_ptr = new_node;

      trie->size++;

      return true;
    }
  } while (string[i] != DELIMITER);

  // If we've arrived here, we've traversed through the entire string and have
  // arrived at a node that already exists.

  // The existing node is a full leaf, so we split it and make it
  // represent our new string.
  if ((*node_ptr)->type == 2) {
    ttnode_split(*node_ptr);
  }
  // The string is already in the trie
  else if ((*node_ptr)->type == 1) {
    return false;
  }

  (*node_ptr)->type = 1;

  trie->size++;

  return true;
}

/**
 * Remove the given string from a TernaryTrie.
 *
 * @param trie trie to remove string from
 * @param string string to remove
 * @return true if the string was in the trie and thus removed, false otherwise
 */
bool ternarytrie_remove(TernaryTrie *trie, const char *string) {
  SearchResult res = ternarytrie_search_node(trie, string);

  if (res.child == NULL) {
    return false;
  }

  trie->size--;

  if (res.parent != NULL) {
    // We're removing a full leaf, so we calculate the offset of the character
    // to remove from the parent
    if (res.child->type == 2) {
      size_t str_len = strlen(string);
      size_t suffix_len = strlen(res.child->ptr.string);

      ttnode_remove(res.parent, string[str_len - suffix_len - 1]);
    }
    // In the other case, the character to remove from the parent is the last
    // character of the string
    else if (res.child->size == 0) {
      size_t i = 0;

      while (string[i + 1] != DELIMITER) {
        i++;
      }

      ttnode_remove(res.parent, string[i]);
    } else {
      res.child->type = 0;

      return true;
    }

    ttnode_free(res.child);
  }
  // We're in the root here
  else {
    res.child->type = 0;
  }

  return true;
}

/**
 * Return the current size of the given trie.
 *
 * @param trie trie to return size for
 * @return size of the trie
 */
size_t ternarytrie_size(TernaryTrie *trie) { return trie->size; }