Advanced Data Structures

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define ARRAY_SIZE(a)  sizeof(a) / sizeof(a[0])

#define ALPHABET_SIZE (26)
/* only use key a-z */
#define CHAR_TO_INDEX(c)   (c - 'a')
#define LEAF_VALUE   1

typedef struct TrieNode_ TrieNode;

struct TrieNode_ {
  int val;
  TrieNode *children[ALPHABET_SIZE];
};

typedef struct Trie_ Trie;
struct Trie_ {
  TrieNode *root;
};

TrieNode *GetNode(void)
{
  TrieNode *pNode;
  pNode = (TrieNode *) malloc(sizeof(TrieNode));

  if(pNode == NULL){
    fprintf(stderr, "malloc failed\n");
    exit (EXIT_FAILURE);
  }
  pNode->val = 0;
  int i ;
  for(i = 0; i < ALPHABET_SIZE; i++){
    pNode->children[i] = NULL;
  }
  return pNode;
}

/* Initialize trie */
void InitialTrie(Trie *pTrie)
{
  pTrie->root = GetNode();
}

/* If not present, insert key into trie.
 * If the key is prefix of trie node, just mark leaf node
 */
void insert(Trie *pTrie, char key[])
{
  int level, index;
  TrieNode *p;
  int length = strlen(key);
  int i;

  if(pTrie->root == NULL)
    InitialTrie(pTrie);
  p = pTrie->root;

  for(level = 0; level < length; level++){
    index = CHAR_TO_INDEX(key[level]);
    if(p->children[index] == NULL)
      p->children[index] = GetNode();
    p = p->children[index];
  }
  p->val = LEAF_VALUE;
}

/* return non zero, if key is in the Trie */
int search(Trie *pTrie, char key[])
{
  int level, index;
  TrieNode *p;
  int length = strlen(key);
  int i;

  if(pTrie->root == NULL)
    return 0;
  p = pTrie->root;
  for(level = 0; level < length; level++){
    index = CHAR_TO_INDEX(key[level]);
    if(p->children[index] == NULL)
      return 0;
    p = p->children[index];
  }
  return ((p != NULL) && (p->val));
}

int main(int argc, char *argv[])
{
  char keys[][8] = {"the", "a", "there", "answer", "any", "by", "bye", "their"};
  Trie trie;
  int i;

  char output[][32] = {"Not present in trie", "Present in trie"};

  InitialTrie(&trie);

    // Construct trie
  for(i = 0; i < ARRAY_SIZE(keys); i++)
  {
    insert(&trie, keys[i]);
  }

    // Search for different keys
  printf("%s --- %s\n", "the", output[search(&trie, "the")] );
  printf("%s --- %s\n", "these", output[search(&trie, "these")] );
  printf("%s --- %s\n", "their", output[search(&trie, "their")] );
  printf("%s --- %s\n", "thaw", output[search(&trie, "thaw")] );
  return 0;
}